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NCERT Solutions for Class 9 Science Chapter 4 Structure of The Atom

NCERT Solutions for Class 9 Science Chapter 4 Structure of The Atom

Edited By Shivani Poonia | Updated on Apr 10, 2025 08:14 AM IST

Everything around us is made up of something and that something behind everything is an atom. From the air we breathe, and the water we drink to the stars, planets, and galaxies everything is made up of small compounds and these compounds are so small that we cannot even see or feel them with the naked eye. To see them we require a microscope. Atoms are the fundamental building block of everything around us from the gold or diamonds used in jewellery to the silicon used in mobile phones.

This Story also Contains
  1. NCERT Solutions for Class 9 Science Chapter 4 Structure of The Atom
  2. Download PDF
  3. NCERT Solutions for Class 9 Science Chapter 4 (In-text Questions)
  4. NCERT solutions for class 9 science chapter 4 (Exercise Questions)
  5. NCERT Solutions for Class 9 Science- Chapter Wise
  6. NCERT Solutions for Class 9 Science: Important Formulas
  7. NCERT Solutions for Class 9 Science Chapter 4 Structure of the Atom - Important Topics
  8. NCERT Books and NCERT Syllabus
  9. NCERT Solutions for Class 9 - Subject Wise

Chapter 4 consists of various important topics like atoms, subatomic particles, and the theories given by famous scientists like Rutherford, Dalton, and Thomson who gave Thomson's model of an atom, etc. NCERT Class 9 Science textbook, aligns with CBSE and other state boards exam syllabus. Questions of different varieties are given in between the text and at the end of every chapter. In this article students get the detailed answer to all the intext and exercise questions of the NCERT textbook.

NCERT Solutions for Class 9 Science Chapter 4 Structure of The Atom

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NCERT Solutions for Class 9 Science Chapter 4 (In-text Questions)

Topic 4.1 Charged particles in the matter? (Page 39)

Q. 1. What are canal rays?

Answer:

Canal rays are the positively charged radiations which consist of positively charged particles of atoms. they can pass through the perforated ( pierced ) cathode and then travel towards another cathode in a gas discharge tube.

They were given the name Canal rays by E. Goldstein in 1866 who discovered these radiations.

Q. 2. If an atom contains one electron and one proton, will it carry any charge or not?

Answer:

The proton is a positively charged particle and the electron is a negatively charged particle. their magnitude is equal and hence net charge in an atom is zero.

Topic 4.2 The structure of an atom ( Page 41)

Q. 1. On the basis of Thomson’s model of an atom, explain how the atom is neutral as a whole.

Answer:

According to Thomson’s model of an atom, an atom consists of a sphere of a positive charge.

The positive charge in the atom is spread all over like the red edible part of a watermelon, while the electrons are studded in the positively charged sphere, just like the seeds in the watermelon.

As negative and positive charges are equal in magnitude, they balance each other and thus the atom becomes electrically neutral as a whole.

Q. 2. On the basis of Rutherford’s model of an atom, which subatomic particle is present in the nucleus of an atom?

Answer:

On the basis of Rutherford’s model of an atom, the subatomic particle which is present in the nucleus of an atom is Proton which is a positively charged particle.

Q. 3. Draw a sketch of Bohr’s model of an atom with three shells.

Answer:

The sketch of Bohr’s model of an atom with three shells:

1651484687087

Q. 4. What do you think would be the observation if the α -particle scattering experiment is carried out using a foil of a metal other than gold?

Answer:

If a foil of a heavy metal like platinum is used, then the observations in the alpha-particle scattering experiment would be the same as that in the gold foil experiment.

If a foil of a light metal like lithium is used, then the observations in the alpha-particle scattering experiment would not be the same because these metal are not so malleable so the thin foil is difficult to obtain.

The problem with not using thin foil is that the number of the alpha particle will bounce back from the thick foil and the location of positive mass would be difficult to find.

Topic 2.4.2 Neutron ( Page 41)

Q. 1. Name the three sub-atomic particles of an atom.

Answer:

The three sub-atomic particles of an atom are :

1. Electron: a negatively charged particle

2. Proton: a positively charged particle

3. Neutron: a neutral particle

Q. 2. Helium atom has an atomic mass of 4 u and two protons in its nucleus. How many neutrons does it have?

Answer:

The atomic mass of Helium = 4 u
No. of protons = 2

As atomic mass = no. of protons + no. of neutrons
No. of neutrons = At. mass - no. of protons
= 4 - 2

= 2

Hence Heium atom has 2 neutrons.

Topic 4.3 How are electrons distributed in different orbits(shells)? ( Page 42)

Q. 1. Write the distribution of electrons in carbon and sodium atoms.

Answer:

Number of electrons in carbon atom = 6

Number of electrons in sodium atom = 11

Electron Distribution:

Element First Orbit or K -shell Second Orbit or L-shell Third Orbit or M-shell
Carbon 2 4 0
Sodium 2 8 1


Q. 2. If K and L shells of an atom are full, then what would be the total number of electrons in the atom?

Answer:

Maximum Number of electrons in K-shell = 2

Maximum Number of electrons in L-shell = 8

The total no. of electrons in the atom = 2 + 8

= 10

If K and L shells of an atom are full, then the total number of electrons in the atom will be 10.

Topic 4.4 Valency (Page- 44 )

Q. 1. How will you find the valency of chlorine, sulphur and magnesium?

Answer:

Valancy is basically the minimum number of the electron we have to add or remove such that every shell in the atom is completely filled.

Mathematically,

when the outermost shell of an atom contains 4 or less than 4 electrons, its valency is equal to the number of valence electrons in the outermost shell and when the outermost shell contains more than 4 electrons, the valency of the atom is equal to 8 - no. of valence electrons in the atom.

Chlorine :

Atomic No. of Cl = 17

Its electronic configuration = 2, 8, 7

Valency of Cl = 8 - 7 = 1

Sulphur :

Atomic no. of S = 16

Its electronic configuration = 2, 8, 6

Valency of S = 8 - 6 = 2

Magnesium:

Atomic no. of Mg = 12

Its electronic configuration = 2, 8, 2

Valency of Mg = 2

Topic 4.5 Atomic number and Mass number ( Page 44)

Q. 1.(i) If the number of electrons in an atom is 8 and the number of protons is also 8, then

(i) what is the atomic number of the atom?

Answer:

Given,

Number of electrons in the atom = 8

Number of proton in the atom = 8

The atomic number of an atom is equal to the number of proton in that atom. hence the atomic number of the given atom is 8.

Q. 1. (ii) If the number of electrons in an atom is 8 and the number of protons is also 8, then

(ii) what is the charge on the atom?

Answer:

In the given atom, the total number of positive charges is equal to the total number of negative charge.

Number of Protons (8) = Number of electrons (8)

They both will neutralize each other. So, the atom will not possess any charge.

Q. 2. With the help of Table 4.1, find out the mass number of oxygen and sulfur atom.

compositions%20of%20Atom

Answer:

For Oxygen:

Number of protons = 8

Number of electrons = 8

Mass number = Number of Protons + Number of neutrons

= 8 + 8

= 16

Hence mass number for Oxygen is 16.

For Sulphur:

Number of protons = 16

Number of electrons = 16

Mass number = Number of Protons + Number of neutrons

= 16 + 16

= 32

Hence Mass number for Sulphur is 32.

Topic 4.6 Isotopes ( Page-45)

Q. 1. For the symbol H,D and T tabulate three sub-atomic particles found in each of them.

Answer:

H, D, and T are the three isotopes of hydrogen with the same atomic number and different mass numbers of 1, 2 and 3 respectively.

Element Symbol Number of Electrons Number of Protons Number of Neutrons
Hydrogen H 1 1 0
Deuterium D 1 1 1
Tritium T 1 1 2


Q. 2. Write the electronic configuration of any one pair of isotopes and isobars.

Answer:

Isotopes :

Isotopes are the atoms with the same number of proton and different atomic mass. The difference in atomic mass arises due to the different number of neutrons present in the atom.

Some Examples of Isotopes are :

1. 12C6 and 14C6 ,

2. 35Cl17 and 37Cl17 .

Isobar:

Isobars are the atom with the same atomic mass and different atomic number.

Some example of Isobars are :

1. 40Ca20 and 40Ar18

2. 22Ne10 and 22Na11

NCERT solutions for class 9 science chapter 4 (Exercise Questions)

Q. 1. Compare the properties of electrons, protons, and neutrons.

Answer:

The Comparison of Properties between Electron, Proton, and Neutron:

Properties Electrons Protons Neutrons
Charge Negatively charged Positively charged No charge
Weight Negligible 1 a.m.u 1 a.m.u
Location in atom Outside the nucleus Inside the nucleus Inside the nucleus
Reaction with a charged particle Attracts positive charge Attracts negative charge gives no reaction to any charge

Q. 2. What are the limitations of J.J. Thomson’s model of the atom?

Answer:

The limitations of J.J. Thomson’s model of the atom are:

1. Thomson's model of the atom could not explain the results of alpha particle scattering experiment carried out by Rutherford. this model failed to depict why most of the alpha particle passes through gold foil and why some of them got diverted in different angles and some of them rebounded and returned back to their paths.

2. It was solely based on the imagination and did not have any experimental evidence.

Q. 3. What are the limitations of Rutherford’s model of the atom?

Answer:

The limitations of Rutherford's model of the atom is that It does not explain the stability of the atom. As we know now, when charged bodies move in a circular motion, they emit radiations.

This means that the electrons revolving around the nucleus (as suggested by Rutherford) would lose energy and come closer and closer to the nucleus, and a stage will come when they would finally merge into the nucleus.

This makes the atom unstable, which is clearly not the case. The electrons do not fall into the nucleus, atoms are very stable and do not collapse on their own.

Q. 4. Describe Bohr’s model of the atom.

Answer:

In order to overcome the objections raised against Rutherford's model of the atom, Neils Bohr put forward his model of the atom. According to Bohr's model of the atom,
1. An atom holds the nucleus in the center. the whole mass of the atom is concentrated at the nucleus.

2. The negatively charged particle revolves around the nucleus in definite circular paths known as orbits or which are designated as K, L, M, N, etc. or numbered as n = 1, 2, 3, 4, etc. (outward from the nucleus).

3. While revolving in discrete orbits, the electrons do not radiate energy. But when an electron jumps from one energy level to another, the energy of the atom changes.


1651477380172

Q. 5. Compare all the proposed models of an atom given in this chapter.

Answer:

Comparison of different proposed Model:

Feature Thomson's Model Rutherford's Model Bohr's Model
Positive Charge The Positive charge is distributed in Sphere The positive charge is concentrated at the core of the atom, which is called the nucleus The positive charge is present in the core of the atom, called nucleus.
Negative Charge The electrons are embedded in the positively charged sphere of an atom, like the seeds in a watermelon. The nucleus is surrounded by electrons, and the electrons and the nucleus are held together by the electrostatic force of attraction The electrons move in discrete orbits, and each orbit is associated with a definite amount of energy.
Limitation This model could not explain the results of an alpha particle scattering experiment This model could not explain the stability of the atom. This model perfectly explains the stability of an atom
Diagrammatic representation 165147743230716514774707851651477487143


Q. 6. Summarise the rules for the writing of the distribution of electrons in various shells for the first eighteen elements.

Answer:

The Bohr and Bury scheme for the distribution of electrons in an atom is based on the following rules :
1. The maximum number of electrons that a shell can have is represented by 2n2 , where n is the quantum number of that particular energy shell. Thus, the maximum number of electrons in the first four shells are :
1st (K) shell 2 x 12 = 2
2nd (L) shell 2 x 22 = 8
3rd (M) shell 2 x 32 = 18
4th (N) shell 2 x 42 = 32

2. The outermost shell, which is also called valence shell, can have a maximum of 8 electrons.

3. If permitted by rule 1, The shell inner to the outermost shell (the second last shell ) can accommodate a maximum of 18 electrons.

4. Electrons are not taken in unless the inner shells are filled, i.e., the shells are filled in a step-wise manner.

Q. 7. Define valency by taking examples of silicon and oxygen.

Answer:

The definite combining capacity of an atom of an element, in which electrons are lost, gained or shared with other atoms to complete the octave in the outermost shell is defined as valency.

In other words,

Valancy is basically the minimum number of the electron we have to add or remove from or in the outermost shell such that every shell in the atom is completely filled.

And Mathematically,

when the outermost shell of an atom contains 4 or less than 4 electrons, its valency is equal to the number of valence electrons in the outermost shell and when the outermost shell contains more than 4 electrons, the valency of the atom is equal to 8 - no. of valence electrons in the atom.

The valency of Silicon:

Atomic number = 14

Distribution of electron :

K = 2

L = 8

M = 4

Number of electrons in outermost shell = 4

Valency = 8 - 4 = 4.

The valency of Oxygen:

Atomic number = 8

Distribution of electrons:

K = 2

L = 6

The number of electron in outermost shell = 6

Valency = 8 - 6 = 2

Q. 8.(i) Explain with examples

(i) Atomic number,

Answer:

Atomic Number :

An atomic number of an atom is the total number of protons present within the nucleus of an atom is known as the atomic number. it is denoted by symbol Z.

Example: As the Oxygen atom has 8 protons in its nucleus, its atomic number is 8.

Q. 8.(ii) Explain with examples

(ii) Mass number,

Answer:

Mass Number :

The mass number of an atom is the sum total of the masses of all the nucleons present in the nucleus of an atom, i.e.,
Mass Number = No. of Protons + No. of Neutrons

It is denoted by A.


Example: As a sodium atom has 11 protons and 12 neutrons in its nucleus,

So, it's mass number = 11 + 12 = 23.

Q. 8.(iii) Explain with examples

(iii) Isotopes

Answer:

Isotopes:

Isotopes are the atoms of the same element having the same atomic number but a different mass number.

Example: Carbon molecule exists as 12C6 and 14C6 .

Q. 8.(iv) Explain with examples

(iv) Isobars.

Answer:

Isobar:

Isobars are the atoms of different elements having the same mass number but different atomic numbers.


Example: 40Ca20 and 40Ar18 . Mass numbers of calcium and argon atoms have different atomic numbers (20 and 18 ) but the same mass number 40.

Two uses of isotopes are:

(i) An isotope of uranium is used as fuel in nuclear reactors.

(ii) An isotope of cobalt is used in the treatment of cancer.

Q. 9. Na+ has completely filled K and L shells. Explain.

Answer:

The atomic number of Na = 11

No. of electrons in Na atom = 11

In Na+ ,the positive charge is obtained due to the loss of one electron from the M shell of Na atom.

So, No. of electrons in Na + ion = 11 -1 = 10

Hence, electronic configuration of Na + = 2, 8

In Na + , K and L shells are completely filled since K shell can have a maximum of 2 electrons and L shell can have a maximum of 8 electrons.

Q. 10. If bromine atom is available in the form of, say, two isotopes 3579Br(49.7o/o) and 3581Br(50.3o/o) , calculate the average atomic mass of bromine atom.

Answer:

Given, two isotopes 3579Br(49.7o/o) and 3581Br(50.3o/o) .

Average atomic mass:

=79×49.7100+81×50.3100

=3926.3100+4074.3100

=8000.6100

=80.006u .

Q. 11. The average atomic mass of a sample of an element X is 16.2u . What are the percentages of isotopes 816X and 818X in the sample?

Answer:

Given, the average atomic mass of a sample of an element X is 16.2u .

Two isotopes of element = 816X and 818X

Now, Let's percent of isotope 816X be x and percent of 818X be 100 - x

So, According to the question,

Average Atomic Mass :

16.2=16×x100+18×100x100

16.2=16x100+1818x100

1.8=2x100

2x=180

x=90

Hence the percentage of isotope 816X is 90 % and thepercentage isotope 816X is 10%.

Q. 12. If Z=3 , what would be the valency of the element? Also, name the element.

Answer:

Given

the Atomic number, Z = 3

Distribution of electrons :

K = 2,

L = 1
So, Valency = 1 .

The element with atomic number 3 is lithium.

Q. 13. Composition of the nuclei of two atomic species X and Y are given as under

X Y

Protons = 6 6

Neutrons = 6 8

Give the mass numbers of X and Y . What is the relation between the two species?

Answer:

As we know,

the mass number of an atom = No. of protons + No. of Neutrons

So,

The mass number of X = No. of protons of X + No. of Neutrons of X

= 6 + 6

= 12

The mass number of Y = No. of protons of Y + No. of Neutrons of Y

= 6 + 8

= 14

As both X and Y have the same atomic number (6) but different numbers (i.e., 12 and 14 respectively), they are isotopes.

Q. 14. For the following statements, write T for True and F for False.

(a) J.J. Thomson proposed that the nucleus of an atom contains only nucleons.

(b) A neutron is formed by an electron and a proton combining together. Therefore, it is neutral.

(c) The mass of an electron is about 1 2000 times that of a proton.

(d) An isotope of iodine is used for making tincture iodine, which is used as a medicine.

Put a tick against correct choice and cross (×) against wrong choice in questions 15, 16 and 17

Answer:

(a) The statement is False.
(b) The statement is False.
(c) The statement is True.
(d) The statement is True.

Q. 15. Rutherford’s alpha-particle scattering experiment was responsible for the discovery of

(a) Atomic Nucleus

(b) Electron

(c) Proton

(d) Neutron

Answer:

Rutherford’s alpha-particle scattering experiment was responsible for the discovery of the Atomic Nucleus.

Hence, option (a) is the correct answer.

Q. 16. Isotopes of an element have

(a) the same physical properties

(b) different chemical properties

(c) different number of neutrons

(d) different atomic numbers

Answer:

Isotopes of an element have a different number of neutrons.

Hence option (c) is correct.

Q. 17. A Number of valence electrons in Cl ion are:

(a) 16

(b) 8

(c) 17

(d) 18

Answer:

The Electronic configuration of Cl ion is :

K = 2

L = 8

M = 8

Hence Number of valance electron in Cl ion = 8.

Hence, option (b) is the correct answer.

Q. 18. Which one of the following is a correct electronic configuration of sodium?

(a) 2,8

(b) 8,2,1

(c) 2,1,8

(d) 2,8,1.

Answer:

The atomic number of sodium = 11

The electronic configuration of the sodium :

K = 2

L = 8

M = 1

Hence, option (d) is correct.

Q. 19. Complete the following table.

Answer:

Atomic NumberMass NumberNumber of NeutronsNumber of ProtonsNumber of ElectronsNumber of Atomic Species
9-10---
1632---Sulphur
-24-12--
-2-1--
-1010-

First row:

atomic number = 9

so, the element is Fluorine.

Atomic no. = No. of protons = no. of electrons = 9

Mass number = no. of protons + no. of neutrons = 9 + 10 = 19

Second row:

Since atomic no. is 16 so, no. of protons = no. of electrons = 16

No. of neutrons = Mass no. - no. of protons = 32 - 16 = 16

Third row:

No. of protons = Atomic no. = 12

So, the element is Magnesium.

No. of electrons = no. of protons = 12

No. of neutrons = Mass no. - no. of protons = 24 - 12 = 12

Fourth row:

No. of protons = Atomic no. = 1

So, the element is Deuterium.

No. of electrons = no. of protons = 1

No. of neutrons = Mass no. - no. of protons = 2 - 1 = 1

Fifth row:

No. of protons = Atomic no. = 1

The element is Protium since the mass number is 1.

So the Table becomes,

Atomic number mass number Number of neutrons Number of protons Number of electrons Name of the element
9 19 10 9 9 Fluorine
16 32 16 16 16 Sulfur
12 24 12 12 12 Magnesium
1 2 1 1 1 Deuterium
1 1 1 1 0 Hydrogen ion


NCERT Solutions for Class 9 Science- Chapter Wise

Chapter No.
Chapter Name
Chapter 1
Matter in Our Surroundings
Chapter 2
Is Matter Around Us Pure
Chapter 3
Atoms and Molecules
Chapter 4
Structure of The Atom
Chapter 5
The Fundamental Unit of Life
Chapter 6
Tissues
Chapter 7
Motion
Chapter 8
Force and Laws of Motion
Chapter 9
Gravitation
Chapter 10
Work and Energy
Chapter 11
Sound
Chapter 12
Improvement in Food Resources


NCERT Solutions for Class 9 Science: Important Formulas

  • Maximum number of electrons in different shells

According to the Bohr model of the atom, the maximum number of electrons that can occupy a shell is given by the formula 2n2, where n represents the shell number. The first shell (n = 1) can hold a maximum of 2 electrons, the second shell (n = 2) can hold a maximum of 8 electrons, and so on.

  • Average atomic mass

Average atomic mass = (M1× P1) + (M2 × P2) + ... + (Mn × Pn)

Where:

M1, M2 ..., and Mn represent the individual atomic masses of the isotopes of the element.

P1, P2 ..., and Pn represent their respective natural abundances as decimal fractions or percentages (converted to decimal form).

NCERT Solutions for Class 9 Science Chapter 4 Structure of the Atom - Important Topics

  • Introduction to atoms: Made up of protons, neutrons, and electrons, atoms are the fundamental units of matter.
  • Charged particles in matter: Matter is composed of positively charged protons, neutral neutrons, and negatively charged electrons.
  • The structure of an atom: Protons and neutrons make up the core nucleus of an atom, which is encircled by orbiting electrons.
  • Thomson's model of the atom: Also known as the "plum pudding" model, Thomson proposed that an atom is a positively charged mass with embedded negatively charged electrons.
  • Rutherford's model of the atom: Rutherford's model suggests that atoms have a tiny, positively charged nucleus at the centre, with electrons orbiting around it.
  • Bohr's model of the atom: Bohr proposed that electrons occupy specific energy levels or orbit around the nucleus, and they jump between these levels by absorbing or emitting energy.
  • Electron distribution in different orbits: Electrons are arranged in different energy levels or electron shells, with lower energy levels closer to the nucleus.

NCERT Books and NCERT Syllabus


NCERT Solutions for Class 9 - Subject Wise


NCERT Science Exemplar Solutions Class 9 - Chapter Wise

Frequently Asked Questions (FAQs)

1. What are the important topics coverd under Class 9 Science NCERT syllabus chapter 4?

The main topics covered in NCERT text book for Class 9 Science chapter 4 are-

  • Concept of Charged Particles in Matter 
  • Different Models of The Atom
  • Neutrons
  • How Are Electrons Distributed in Different Orbits
  • Valency, Atomic Number and Mass Number.
2. What are the main components of an atom?

The main components of an atom are protons, neutrons, and electrons. Protons and neutrons are located in the nucleus, while electrons orbit around the nucleus.

3. How do isotopes differ from each other?

Isotopes are atoms of the same element that have the same number of protons but differ in the number of neutrons. This results in isotopes having different mass numbers.

4. What are the different atomic models discussed in this chapter?

The chapter discusses several atomic models, including Thomson's plum pudding model, Rutherford's nuclear model, and Bohr's model of the atom.

5. What are the postulates of Dalton’s Atomic Theory?

The postulates of Dalton’s Atomic theory are : 

  • All matter is made up of atom
  • Atoms can neither be created and nor be destroyed 
  • Atoms of same elements are identical in mass and chemical properties
  • Atoms of different elements have different mass and different chemical properties 
6. What are the limitations of Rutherford’s model of the atom?

The limitations of Rutherford’s model of atom are:

  • Unable to explain the stability of atom
  • Did not explain the electron spectra 
  • The model did not explain how electrons are distributed around the nucleus.

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A block of mass 0.50 kg is moving with a speed of 2.00 ms-1 on a smooth surface. It strikes another mass of 1.00 kg and then they move together as a single body. The energy loss during the collision is

Option 1)

0.34\; J

Option 2)

0.16\; J

Option 3)

1.00\; J

Option 4)

0.67\; J

A person trying to lose weight by burning fat lifts a mass of 10 kg upto a height of 1 m 1000 times.  Assume that the potential energy lost each time he lowers the mass is dissipated.  How much fat will he use up considering the work done only when the weight is lifted up ?  Fat supplies 3.8×107 J of energy per kg which is converted to mechanical energy with a 20% efficiency rate.  Take g = 9.8 ms−2 :

Option 1)

2.45×10−3 kg

Option 2)

 6.45×10−3 kg

Option 3)

 9.89×10−3 kg

Option 4)

12.89×10−3 kg

 

An athlete in the olympic games covers a distance of 100 m in 10 s. His kinetic energy can be estimated to be in the range

Option 1)

2,000 \; J - 5,000\; J

Option 2)

200 \, \, J - 500 \, \, J

Option 3)

2\times 10^{5}J-3\times 10^{5}J

Option 4)

20,000 \, \, J - 50,000 \, \, J

A particle is projected at 600   to the horizontal with a kinetic energy K. The kinetic energy at the highest point

Option 1)

K/2\,

Option 2)

\; K\;

Option 3)

zero\;

Option 4)

K/4

In the reaction,

2Al_{(s)}+6HCL_{(aq)}\rightarrow 2Al^{3+}\, _{(aq)}+6Cl^{-}\, _{(aq)}+3H_{2(g)}

Option 1)

11.2\, L\, H_{2(g)}  at STP  is produced for every mole HCL_{(aq)}  consumed

Option 2)

6L\, HCl_{(aq)}  is consumed for ever 3L\, H_{2(g)}      produced

Option 3)

33.6 L\, H_{2(g)} is produced regardless of temperature and pressure for every mole Al that reacts

Option 4)

67.2\, L\, H_{2(g)} at STP is produced for every mole Al that reacts .

How many moles of magnesium phosphate, Mg_{3}(PO_{4})_{2} will contain 0.25 mole of oxygen atoms?

Option 1)

0.02

Option 2)

3.125 × 10-2

Option 3)

1.25 × 10-2

Option 4)

2.5 × 10-2

If we consider that 1/6, in place of 1/12, mass of carbon atom is taken to be the relative atomic mass unit, the mass of one mole of a substance will

Option 1)

decrease twice

Option 2)

increase two fold

Option 3)

remain unchanged

Option 4)

be a function of the molecular mass of the substance.

With increase of temperature, which of these changes?

Option 1)

Molality

Option 2)

Weight fraction of solute

Option 3)

Fraction of solute present in water

Option 4)

Mole fraction.

Number of atoms in 558.5 gram Fe (at. wt.of Fe = 55.85 g mol-1) is

Option 1)

twice that in 60 g carbon

Option 2)

6.023 × 1022

Option 3)

half that in 8 g He

Option 4)

558.5 × 6.023 × 1023

A pulley of radius 2 m is rotated about its axis by a force F = (20t - 5t2) newton (where t is measured in seconds) applied tangentially. If the moment of inertia of the pulley about its axis of rotation is 10 kg m2 , the number of rotations made by the pulley before its direction of motion if reversed, is

Option 1)

less than 3

Option 2)

more than 3 but less than 6

Option 3)

more than 6 but less than 9

Option 4)

more than 9

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