The standard enthalpy of formation of NH₃ is– 46.0 kJmol^–1. If the enthalpy of formation of H₂ from its atoms is – 436 kJ mol^–1 and that of N₂ is – 712 kJ mol^–1,the average bond enthalpy of N – H bond is NH₃ is

• -964 kJ mol^-1

• +352 kJ mol^-1

• +1056 kJ mol^-1

• +1056 kJ mol^-1

Consider the reaction:
Cl₂(aq) + H₂S(aq) → S (s) + 2H⁺ (aq) + 2Cl^- (aq)
The rate equation for this reaction is
I. Cl₂ + H₂S → H⁺ +Cl^- + Cl⁺ +HS^-
II. H₂S ⇌ H⁺ + HS^- (fast equilibrium)
Cl₂ + HS^- → 2Cl^- + H⁺ + S (slow)

• II only

• Both (I) and (II)

• Neither (I) nor (II)

• Neither (I) nor (II)

If 10^–4 dm³ of water is introduced into a 1.0 dm³ flask at 300 K, how many moles of water are in the vapour phase when equilibrium is established?(Given: Vapour pressure of H₂O at 300 K is 3170 P_a; R = 8.314 J K^–1 mol^–1)

• 5.56 x 10^-3 mol

• 1.53 x 10^-2 mol

• 4.46 x 10^-2 mol

• 4.46 x 10^-2 mol

The energy required to break one mole of Cl— Cl bonds in Cl2 is 242 kJ mol^–. The longest wavelength of light capable of breaking a single Cl — Cl bond is
(c= 3 x 10⁸ ms^–1and N_A = 6.02 x 10²³ mol^–1)

• 594 nm

• 640 nm

• 700 nm

• 700 nm

The ionization energy of He+ is 19.6 x 10–18 J atom^–1. The energy of the first stationary state (n = 1) of Li²⁺ is

• 4.41 x 10^-16 J atom^–1

• -4.41 x 10^-17 J atom^–1

• -2.2 x 10^-15 J atom^–1.

• -2.2 x 10^-15 J atom^–1.

Three reactions involving H₂PO₄^- are given below
I. H₃PO₄ + H₂O → H₃O⁺ + H₂PO₄^-
II. H₂PO₄^- + H₂O→ HPO₄^2- + H₃O⁺
III. H₂PO₄^- + OH^- → H₃PO₄  + O^2-
In which of the above does H₂PO₄^- act  as an acid

• (II) only

• (I) and (II)

• (III) only

• (III) only

In aqueous solution the ionization constants for carbonic acid are
K₁ = 4.2 x 10^-7 and K₂ = 4.8 x 10^-11.
Select the correct statement for a saturated 0.034 M solution of the carbonic acid.

• The concentration of CO₃^2- is 0.034 M

• The concentration of CO₃^2- is greater than that of HCO₃^-

• The concentration of H⁺ and HCO₃^- are approximately equal

• The concentration of H⁺ and HCO₃^- are approximately equal

The correct order of increasing basicity of the given conjugate bases (R = CH₃) is

The correct sequence which shows decreasing order of the ionic radii of the elements is

• Al³⁺ > Mg²⁺ > Na⁺ > F^- > O^2-

• Na⁺ > Mg²⁺ > Al³⁺ > O^2- > F^-

• Na⁺ > F^- > Mg²⁺ > O^2- > Al³⁺

• Na⁺ > F^- > Mg²⁺ > O^2- > Al³⁺

The solubility product of silver bromide is 5.0 x 10^-13. The quantity of potassium bromide (molar mass taken as 120 g mol^–1)to be added to 1 litre of 0.05 M solution of silver nitrate to start the precipitation of AgBr is

• 1.2 x 10^-10 g 

• 1.2 x 10^-9 g

• 6.2 x 10^-5 g 

• 6.2 x 10^-5 g