CBSE Class 10 Science Question Paper 2025 with Solutions, Download Set-Wise PDF

CBSE 10th Science Question Paper With Solution 2025

SECTION- A | Code- 31/4/1

Q1. In which one of the following situations a chemical reaction does not occur?

(a) Milk is left open at room temperature during summer

(b) Grapes get fermented

(c) An iron nail is left exposed to a humid atmosphere

(d) Melting of glaciers

Ans.

Explanation:
A chemical reaction involves the formation of new substances with different properties. Let's analyze each option:
(a) Milk is left open at room temperature during summer $\to$ A chemical reaction occurs because the milk undergoes spoiling due to bacterial action.
(b) Grapes get fermented $\to$ A chemical reaction occurs as sugars in grapes convert into alcohol due to fermentation.
(c) An iron nail is left exposed to a humid atmosphere $\to$ A chemical reaction occurs as iron reacts with oxygen and moisture to form rust (iron oxide).
(d) Melting of glaciers $\to$ No chemical reaction occurs because melting is a physical change, where water changes from solid to liquid without forming a new substance.

Thus, the melting of glaciers is a physical change, not a chemical reaction.

Hence, the answer is option (d).

Q2. In order to prepare dry hydrogen chloride gas in a humid atmosphere the gas produced is passed through a guard tube (drying tube) which contains the:
(a) Calcium chloride
(b) Calcium oxide
(c) Calcium hydroxide
(d) Calcium carbonate

Ans.

Explanation:
To prepare dry hydrogen chloride $(\mathrm{HCl})$ gas in a humid atmosphere, the gas must be passed through a drying agent that absorbs moisture. Let's analyze the options:
(a) Calcium chloride $\left({\mathrm{CaCl}}_2\right)\to$ A strong hygroscopic substance (absorbs water) and is commonly used as a drying agent. $✓$ Correct Answer
(b) Calcium oxide $(\mathrm{CaO})\to$ Also absorbs moisture but reacts with acidic gases like HCl , forming calcium hydroxide.
(c) Calcium hydroxide $(\mathrm{Ca}(\mathrm{OH}{)}_2)\to$ A base that would react with HCl , neutralizing it and forming calcium chloride and water.
(d) Calcium carbonate $\left({\mathrm{CaCO}}_3\right)\to$ Reacts with ${\mathrm{HCl}}_{\text{r}}$ producing carbon dioxide $\left({\mathrm{CO}}_2\right)$ and water, making it unsuitable for drying HCl gas.

Thus, anhydrous calcium chloride $\left({\mathrm{CaCl}}_2\right)$ is the best choice for removing moisture without reacting with HCl gas.

Hence, the answer is the option (a).

Q3. The property by virtue of which a solid material can be drawn into thin wires is called :
(a) malleability
(b) ductility
(c) rigidity
(d) resistivity

Ans.

Explanation:
Ductility is the property of a material that allows it to be drawn into thin wires without breaking. Metals like gold, silver, and copper are highly ductile. Correct Answer
Malleability refers to the ability of a material to be hammered or rolled into thin sheets without breaking (e.g., gold, aluminum).
Rigidity refers to the resistance of a material to deformation under applied force. A highly rigid material does not easily bend or stretch.
Resistivity is the measure of how strongly a material opposes the flow of electric current. It is related to electrical properties, not mechanical properties.

Thus, the correct answer is ductility.

Hence, the answer is the option (b).

Q4. Select from the following a hydrocarbon having one $\mathrm{C}-\mathrm{C}$ bond and one $\mathrm{C}=\mathrm{C}$ bond :
(a) Benzene
(b) Cyclohexane
(c) Butyne
(d) Propyne

Ans.

Explanation:
We need to identify a hydrocarbon that contains:
- One C-C single bond
- One C三C triple bond

Let's analyze each option:
1. (a) Benzene $\left({\mathrm{C}}_6{\mathrm{H}}_6\right)\to$ Contains an aromatic ring with alternating single and double bonds, but no C $\equiv$ C triple bond.
2. (b) Cyclohexane $\left({\mathrm{C}}_6{\mathrm{H}}_{12}\right)\to \mathrm{A}$ fully saturated cyclic compound with only $\mathrm{C}-\mathrm{C}$ single bonds, no $\mathrm{C}\equiv \mathrm{C}$ triple bond.
3. (c) Butyne $\left({\mathrm{C}}_4{\mathrm{H}}_6\right)\to$ There are two isomers:
1-Butyne $(\mathrm{CH}\equiv \mathrm{C}-{\mathrm{CH}}_2-{\mathrm{CH}}_3)\to$ Has one $\mathrm{C}\equiv \mathrm{C}$ triple bond and a $\mathrm{C}-\mathrm{C}$ single bond
2-Butyne $({\mathrm{CH}}_3-\mathrm{C}\equiv \mathrm{C}-{\mathrm{CH}}_3)\to$ Only has a triple bond between two central carbons, no clear CC single bond separately.
Since the isomer is not specified, we need a more certain choice.
4. (d) Propyne $({\mathrm{C}}_3{\mathrm{H}}_4,\mathrm{CH}\equiv \mathrm{C}-{\mathrm{CH}}_3)\to$ Clearly has:
One CEC triple bond between the first two carbon atoms
One C-C single bond between the second and third carbon atoms
Correct Answer

Hence, the answer is the option (d).

Q5. The essential element taken up from the soil by the plants to synthesize proteins is :
(a) Phosphorus
(b) Nitrogen
(c) Iron
(d) Magnesium

Ans.

Explanation:
Nitrogen $(\mathrm{N})$ is an essential nutrient required for plants to synthesize proteins because it is a major component of amino acids, which are the building blocks of proteins.
Plants absorb nitrogen from the soil primarily in the form of nitrate $\left({\mathrm{NO}}_3{-}^{}\right)$or ammonium $\left({\mathrm{NH}}_4{+}^{}\right)$ ions.
Nitrogen is also a key component of chlorophyll, nucleic acids (DNA, RNA), and enzymes, making it crucial for plant growth.

Why not the other options?
(a) Phosphorus (P): Important for ATP, DNA, and RNA synthesis, but not directly for protein formation.
(c) Iron (Fe): Essential for chlorophyll synthesis and enzyme activation, but not a primary component of proteins.
(d) Magnesium (Mg): A key component of chlorophyll and enzyme activation, but does not directly contribute to protein synthesis.

Hence, the answer is the option (b).