The hydrides of the first elements in groups 15-17, namely NH₃, H₂O and HF respectively show abnormally high values for melting and boiling points. This is due to

• small size of N, O and F

• the ability to form extensive intermolecular H-bonding

• the ability to form extensive intramolecular H-bonding

• effective van der Waals' interaction

The quantity of electricity needed to separately electrolyze 1 M solution of ZnSO₄ , AlCl₃ and AgNO₃ completely is in the ratio of

• 2 : 3 : 1

• 2 : 1 : 1

• 2 : 1 : 3

• 2 : 2 : 1

The amount of electrolytes required to coagulate a given amount of AgI colloidal solution (-ve charge) will be in the order

• NaNO₃ > Al₂(NO₃)₃ > Ba(NO₃)₂

• Al₂(NO₃)₃ > Ba(NO₃)₂ > NaNO₃

• Al₂(NO₃)₂ > NaNO₃ > Ba(NO₃)₂

• NaNO₃ > Ba(NO₃)₂ > Al₂(NO₃)₃

Among the following observations, the correct one that differentiates between SO${}_3^{2-}$ and SO${}_4^{2-}$ is

• both form precipitate with BaCl₂, SO${}_3^{2-}$ dissolves in HCl but SO${}_4^{2-}$ does not

• SO${}_3^{2-}$ forms precipitate with BaCl₂, SO${}_4^{2-}$ does not

• SO${}_4^{2-}$ forms precipitate with BaCl₂, SO${}_3^{2-}$ does not

• both form precipitate with BaCl₂, SO${}_4^{2-}$ dissolves in HCl but SO${}_3^{2-}$ does not

The two half-cell reactions of an electrochemical cell is given as

Ag⁺ + e^- → Ag; ${\mathrm{E}}_{{\mathrm{Ag}}^{+}/ \mathrm{Ag}}^{°}$ = -0.3995 V

Fe²⁺ → Fe³⁺ + e^- ; ${\mathrm{E}}_{{\mathrm{Fe}}^{3+}/ {\mathrm{Fe}}^{2+}}^{°}$ = -0.7120 V

The value of cell EMF will be

• -0.3125 V

• 0.3125 V

• 1.114 V

• -1.114 V

At 25°C, the molar conductance of 0.007 M hydrofluoric acid is 150 mho cm²mol^-1 and its Λ°_m = 500 cm²mol^-1. The value of the dissociation constant of the acid at the given concentration at 25°C is

• 7 × 10^-4 M

• 7 × 10^-5 M

• 9 × 10^-3 M

• 9 × 10^-4 M

To observe an elevation of boiling point of 0.05°C, the amount of a solute (mol. wt. = 100) to be added to 100 g of water (K_b = 0.5) is

• 2 g

• 0.5 g

• 1 g

• 0.75 g

A piece of wood from an archaeological sample has 5.0 counts min^-1 per gram of C-14, while a fresh sample of wood has a count of 15.0 min^-1g^-1. If half-life of C-14 is 5770 yr, the age of the archaeological sample is

• 8,500 yr

• 9,200 yr

• 10,000 yr

• 11,000 yr

49.

Two gases X (molecular weight M_x) and Y (molecular weight M_y; M_Y > M_X) are at the same temperature T in two different containers. Their root mean square velocities are C_X and C_Y respectively. If the average kinetic energies per molecule of two gases X and Y are E_X and E_Y respectively then which of the following realation(s) is (are) true?

• E_X > E_Y

• C_X > C_Y

• E_X = E_Y = (3/2) RT

• E_X = E_Y = (3/2) k_BT

The formal potential of Fe³⁺ /Fe²⁺ in a sulphuric acid and phosphoric acid mixture (E° = +0.61 V) is much lower than the standard potential (E° = +0.77 V). This is due to

• formation of the species [FeHPO₄]⁺

• lowering of potential upon complexation

• formation of the species [FesO₄]+

• high acidity of the medium