CBSE 12th Pre-Board Exams Date Sheet 2025-26 - Check Official Timings, Schedule Here

what is the difference between nucleophilicity and basicity?

5) During a trekking activity of 6km a student Ram will go to Sangam and return back up to 12 noon. He estimates that he can go to the Sangam at 1.5km/h on average, and return at half of that speed. These speeds take into account breaks and rest times. Using Ram's estimated speeds, what is the latest time he can begin his walk so that he can return by 12 noon?

(a) State the reasons for which Hershey and Chase carried out their experiments.
(b) Answer the following questions based on the experiments of Hershey and Chase :
(i) Name the different radioactive isotopes they used, and explain how they used them.
(ii) Why did they need to agitate and spin their culture ?
(iii) Write their observations and the conclusions they arrived at.

While studying the dependence of potential difference (V) across a resistor on the current (I) passing through it, in order to determine the resistance of the resistor, a student took 5 readings for different values of current and plotted a graph between V and I . He got a straight line graph passing through the origin. What does the straight line signify ? Write the method of determining resistance of the resistor using this graph.

A student holding a mirror in his hand, directed the reflecting surface of the mirror towards the Sun. He then directed the reflected light on to a sheet of paper held close to the mirror.

(a) What should he do to burn the paper ?

(b) Which type of mirror does he have ?

(c) Will he be able to determine the approximate value of focal length of this mirror from this activity ? Give reason and draw ray diagram to justify your answer in this case. 

formula of 3rd law of thermodynamics

A student while observing an embryo of a pen seed in the laboratory listed various parts of the embryo as given below : 

Testa, tegmen, radicle, Plumule, micropyle, cotyledon

On examining the list the teacher remarked that only three parts are correct. Select three correct parts from the above list

a) tests, Radicle, cotyledons    b) Tegmen, Radicle, Microphyle

c) cotyledons, plumule, Testa    d) Radicel, cotyledons, plumule

Two identical billiard balls strike a rigid wall with the same speed but at different angles, and get reflected without any change in speed, as shown in Fig. 5.6. What is (i) the direction of the force on the wall due to each ball? (ii) the ratio of the magnitudes of impulses imparted to the balls by the wall ?

A police jeep on a petrol duty on national highway was moving with a speed of 54km/hr. in the same direction. It finds a thief rushing up in a car at a rate of 126km/hr in the same direction. Police sub – inspector fired at the car of the thief with his service revolver with a muzzle speed of 100m/s. with what speed will the bullet hit the car of thief? CLASS - XI PHYSICS (Kinematics)

How many of the following points satisfy the inequality 2x-3y≤ -5?

A.  (0, -1)

B. (0, 1)

C. (-4, 0)

D. (4, 0)