List of top Questions asked in CBSE CLASS XII

If \[ \begin{bmatrix} 3 & -1 \\ 0 & 1 \\ 2 & -3 \end{bmatrix} A = \begin{bmatrix} 2 & -5 \\ -17 \end{bmatrix} \] then find matrix \( A \).
In a Linear Programming Program (LPP) for objective function \( Z = 14x - 10y \) subject to the constraints: \[ x + y \leq 8, \quad 3x - 2y \geq -6, \quad x, y \geq 0 \] shade the feasible region and mark the corner points in a neatly drawn graph.
\[ \int \frac{a^x}{\sqrt{1 - a^2 x}} \, dx \] is equal to :
If \( f(x) = -2x^8 \), then the correct statement is :
\[ \int \frac{e^{9 \log x} - e^{8 \log x}}{e^{6 \log x}} \, dx \] is equal to :
A student tries to tie ropes, parallel to each other from one end of the wall to the other. If one rope is along the vector \( \hat{i} + 15 \hat{j} + 6 \hat{k} \) and the other is along the vector \( 2 \hat{i} + 10 \hat{j} + 6 \hat{k} \), then the value of \( \lambda \) is :
If \( R \) be a relation defined as \( a \, R \, b \) iff \( |a - b|>0 \), \( a, b \in \mathbb{R} \), then \( R \) is :
If \[ \begin{bmatrix} 2x-1 & 3x \\ 0 & y^2-1 \end{bmatrix} = \begin{bmatrix} x+3 & 12 \\ 0 & 35 \end{bmatrix} \] then the value of \( (x - y) \) is :
Explain how the immunity of a person is affected if there is atrophy (degeneration) of the thymus gland at an early stage of life.
Why are restrictions imposed on MTP in India? Up to how many weeks or trimesters, is MTP considered relatively safe for a female, if necessary to perform, by a medical practitioner?
According to the generally accepted definition of the ideal solution there are equal interaction forces acting between molecules belonging to the same or different species. (This is equivalent to the statement that the activity of the components equals the concentration.) Strictly speaking, this concept is valid in ecological systems (isotopic mixtures of an element, hydrocarbons mixtures, etc.). It is still usual to talk about ideal solutions as limiting cases in reality since very dilute solutions behave ideally with respect to the solvent. This law is further supported by the fact that Raoult’s law empirically found for describing the behaviour of the solvent in dilute solutions can be deduced thermodynamically via the assumption of ideal behaviour of the solvent.
Ribose and 2-deoxyribose have an important role in biology. Among the most important derivatives are those with phosphate groups attached at the 5 position. Mono-, di- and tri-phosphate forms are important, as well as 3-5 cyclic monophosphates. Purines and pyrimidines form an important class of compounds with ribose and deoxyribose. When these purine and pyrimidine derivatives are coupled to a ribose sugar, they are called nucleosides.
Reactant ‘A’ underwent a decomposition reaction. The concentration of ‘A’ was measured periodically and recorded in the table given below:
Time (Hours)[A] (M)
00.40
10.20
20.10
30.05
Based on the above data, predict the order of the reaction and write the expression for the rate law.
Calculate the cell voltage of the voltaic cell which is set up by joining the following half-cells at 25°C:
Al/Al3+ (0.002 M) and Ni/Ni2+ (0.002 M)
Given: \( E^\circ_{\text{Ni}^{2+}/\text{Ni}} = -0.25 \, \text{V} \)
\( E^\circ_{\text{Al}^{3+}/\text{Al}} = -1.66 \, \text{V} \)
\( \log 5 = 0.6990 \)

An aromatic compound ‘A’ with molecular formula C8H8O gives positive 2,4-DNP test. It gives yellow precipitate of compound ‘B’ on treatment with sodium hypoiodite. Compound ‘A’ does not react with Tollen’s or Fehling’s reagent; on drastic oxidation with KMnO4 it forms a carboxylic acid ‘C’. Elucidate the structures of A, B, and C. Also give their IUPAC names.

For the reaction:
2H$_2$O$_2$ $\xrightarrow{I^-}$ 2H$_2$O + O$_2$
Given mechanism:
(I) H$_2$O$_2$ + I$^-$ → H$_2$O + IO$^-$ (slow)
(II) H$_2$O$_2$ + IO$^-$ → H$_2$O + I$^-$ + O$_2$ (fast)
(1) Write rate law for the reaction.
(2) Write the overall order and molecularity of the reaction.
Arrange the following compounds as asked:
(a) In decreasing order of pKb values
C2H5NH2, (C2H5)2NH, C6H5NHCH3, C6H5NH2
(b) In increasing order of boiling point
C2H5OH, C2H5NH2, (CH3)2NH
(c) In increasing order of solubility in water
C6H5NH2, (C2H5)2NH, C2H5NH2

The reaction between A2 (g) and B2 (g) was carried out in a sealed isothermal container. The rate law for the reaction was found to be:

Rate = \( k[\text{A}_2][\text{B}_2] \)

If 1 mole of A2 (g) was added to the reaction chamber and the temperature was kept constant, then predict the change in rate of the reaction and the rate constant.

Give explanation for each of the following observations:

(a) With the same d-orbital configuration (d4), Mn3+ ion is an oxidizing agent whereas Cr2+ ion is a reducing agent.

(b) Actinoid contraction is greater from element to element than that among lanthanoids.

(c) Transition metals form a large number of interstitial compounds with H, B, C, and N.

Identify and draw the main products formed in the following chemical reactions:
Name and define the cell which was used for providing electric power in the Apollo space programme. Also write its one advantage.
A compound ‘A’ with molecular formula C4H8O gives positive 2,4-DNP test. It gives yellow precipitate of compound ‘B’ on treatment with sodium hydrogen sulphite. Compound ‘A’ does not react with Tollen’s or Fehling’s reagent; on oxidation with KMnO4, it forms carboxylic acid ‘C’. Elucidate the structures of ‘A’, ‘B’ and ‘C’. Also give their IUPAC names.

Out of Ti3+, Cr3+, Fe2+ and Ni2+ ions, the one which is the most stable ion in aqueous solution is:

Which of the following properties of transition metals enables them to behave as catalysts?

Name the type of isomerism exhibited and draw isomers:

(I) [Co(NH3)6][Cr(CN)6]

(II) [Co(en)3]3+

(III) [Co(NH3)3(NO2)3]