Science (English Medium) कक्षा १२ - CBSE Important Questions

Explain, giving three reasons, why tropics show greatest levels of species diversity.

An element has atomic mass 93 g mol⁻¹ and density 11.5 g cm^–3. If the edge length of its unit cell is 300 pm, identify the type of unit cell. (N_A = 6.023 × 10²³ mol⁻¹)

Calculate the number of unit cells in 8.1 g of aluminium if it crystallizes in a f.c.c. structure. (Atomic mass of Al = 27 g mol^–1)

Give reasons:Ferrimagnetic substances show better magnetism than antiferromagnetic substances.

Calculate the e.m.f. of the following cell at 298 K:

Fe(s) | Fe²⁺ (0.001 M) | | H⁺ (0.01 M) | H₂(g) (1 bar) | Pt(s)

Given that \[\ce{E^0_{cell}}\] = 0.44 V

[log 2 = 0.3010, log 3 = 0.4771, log 10 = 1]

Calculate the degree of dissociation (α) of acetic acid if its molar conductivity (Λ_m) is 39.05 S cm² mol⁻¹.

(Given \[\ce{\lambda^{\circ}_{(H^+)}}\] = 349.6 S cm² mol⁻¹ and \[\ce{\lambda^{\circ}_{(CH_3COO^-)}}\] = 40.95 S cm² mol⁻¹)

Account for the following:

E° value for the Mn³⁺/Mn²⁺ couple is highly positive (+1.57 V) as compare to Cr³⁺/Cr²⁺.

Which of the following cell was used in the Apollo space programme?

For a reaction A + B ⟶ P, the rate is given by

Rate = k [A] [B]²

How is the rate of reaction affected if the concentration of B is doubled?

For a reaction A + B ⟶ P, the rate is given by

Rate = k [A] [B]²

What is the overall order of reaction if A is present in large excess?

For a chemical reaction R → P, the variation in the concentration (R) vs. time (t) plot is given as:

(i) Predict the order of the reaction.

(ii) What is the slope of the curve?

(iii) Write the unit of rate constant for this reaction.

A first-order reaction is 50% complete in 30 minutes at 300 K and in 10 minutes at 320 K. Calculate activation energy (E_a) for the reaction. [R = 8.314 J K⁻¹ mol⁻¹]

[Given: log 2 = 0.3010, log 3 = 0.4771, log 4 = 0.6021]

Account for the following:

Mn shows the highest oxidation state of +7 with oxygen but with fluorine, it shows oxidation state of +4.

Account for the following:

Cu⁺² salts are coloured, while Zn²⁺ salts are white.

Give a reason for the following: 

Actinoids show irregularities in their electronic configurations.

Give an example and suggest a reason for the following feature of the transition metal chemistry:

The lowest oxide of transition metal is basic, the highest is amphoteric/acidic.

Account for the following:

Mn²⁺ is more stable than Fe²⁺ towards oxidation to +3 state.

Why \[\ce{HCl}\] should not be used for potassium permanganate titrations?

Account for the following:

Transition metals form alloys.

Account for the following:

Sc³⁺ is colourless whereas Ti³⁺ is coloured in an aqueous solution.