List of top Questions asked in CBSE CLASS XII

The time required for 10% completion of a first order reaction at 298 K is equal to that required for its 25% completion at 308 K. If the value of A is \(4 \times 10^{10} s^{-1}\) . Calculate \(k\) at 318 K and \(E_a\).
The oxidation number of cobalt in \(K[Co(CO)_4]\) is
The following data were obtained during the first order thermal decomposition of \(SO_2Cl_2\) at a constant volume.
\(SO_2Cl_2(g) → SO_2(g) + Cl_2(g)\)
ExperimentTime/s-1Total pressure/atm
100.5
21000.6
Calculate the rate of the reaction when total pressure is 0.65 atm.
Predict the products of electrolysis in each of the following: 
 (i) An aqueous solution of AgNO3 with silver electrodes. 
 (ii) An aqueous solution of AgNO3 with platinum electrodes. 
 (iii) A dilute solution of H2SO4 with platinum electrodes. 
 (iv) An aqueous solution of CuCl2 with platinum electrodes.
What are transgenic bacteria? Illustrate using any one example.

Using the property of determinants and without expanding, prove that: \(\begin{vmatrix}a-b&b-c&c-a\\b-c&c-a&a-b\\c-a&a-b&b-c\end{vmatrix}\)=0

An antifreeze solution is prepared from 222.6 g of ethylene glycol C2H6O2 and 200 g of water. Calculate the molality of the solution. If the density of the solution is 1.072 g mL–1, then what shall be the molarity of the solution?
How did Douglas overcome his fear of water?
\(∫\frac{dx}{e^x+e^{-x}}\) is equal to
An edge of a variable cube is increasing at the rate of \(3 cm/s\). How fast is the volume of the cube increasing when the edge is \(10 cm\) long?
A Cassegrain telescope uses two mirrors as shown in Fig. 9.26. Such a telescope is built with the mirrors 20 mm apart. If the radius of curvature of the large mirror is 220 mm and the small mirror is 140 mm, where will the final image of an object at infinity be?
A Cassegrain telescope uses two mirrors
Fig. 9.26
Although the details of the structure of monoclinic sulphur are not well known it probably consists of
Find the projection of the vector \(\hat{i}+3\hat{j}+7\hat{k}\) on the vector \(7\hat{i}-\hat{j}+8\hat{k}.\)
Crystals of Bt toxin produced by some bacteria do not kill the bacteria themselves because -
Draw a well-labelled diagram of an antibody molecule.
What role does the molecular interaction play in a solution of alcohol and water?

In each of the following cases, state whether the function is one-one, onto or bijective. Justify your answer.

  1. f : R→R defined by f(x)=3−4x
  2. f : R→R defined by f(x)=1+x2

Write chemical reaction for the preparation of phenol from chlorobenzene. 

If A and B are square matrices of the same order such that \(AB=BA\),then prove by induction that \(AB^n=B^nA\).Further, prove that \((AB)^n=A^nB^n\) for all \(n∈N\)
A 60 μF capacitor is connected to a 110 V, 60 Hz ac supply. Determine the rms value of the current in the circuit
What do you think is the significance of reproductive health in a society?
Find x, if \(\begin{bmatrix} x &-5&-1 \end{bmatrix}\)\(\begin{bmatrix} 1 & 0 & 2\\ 0 & 2 & 1 \\2&1&3 \end{bmatrix}\)\(\begin{bmatrix} x \\ 4\\1 \end{bmatrix}=O\)
What is spermatogenesis? Briefly describe the process of spermatogenesis.

Three electrolytic cells A,B,C containing solutions of ZnSO4, AgNO3 and CuSO4, respectively are connected in series. A steady current of 1.5 amperes was passed through them until 1.45 g of silver deposited at the cathode of cell B. How long did the current flow? What mass of copper and zinc were deposited?

A coin is biased so that the head is 3 times as likely to occur as tail.If the coin is tossed twice,find the probability distribution of number of tails.