31.

Which of the following statements, about the advantage of roasting of sulphide ore before reduction is not true?

• Carbon and hydrogen are suitable reducing agent for metal sulphides

• The Δ_fG^o of the sulphide is greater than those for CS₂ and H₂S

• The Δ_fG^o  is negative for roasting of sulphide ore to oxide

• The Δ_fG^o  is negative for roasting of sulphide ore to oxide

If 60% of a first order reaction was completed in 60 min, 50% of the same reaction would be completed in approximately:

• 50 min

• 45 min

• 60 min

• 60 min

The equilibrium constant of the reaction:

Cu (s) + 2 Ag⁺ (aq) →  Cu²⁺ (aq) + 2 Ag (s);

E^o = 0.46 V at 298 K

• 2.4 x 10¹⁰

• 2.0 x 10¹⁰

• 4.0 x 10¹⁰

• 4.0 x 10¹⁰

Sulphide ores of metals are usually concentrated by froth flotation process. Which one of the following sulphide ores offers an exception and is concentrated by chemical leaching?

• Argentite

• Galena

• Copper pyrite

• Copper pyrite

The efficiency of a fuel cell is given by:

If NaCl is doped with 10^-4 mol% of SrCl₂ the concentration of cation vacancies will be 
(N_A = 6.02 x 10²³ mol^-1):

• 6.02 x 10¹⁵ mol^-1

• 6.02 x 10¹⁶ mol^-1

• 6.02 x 10¹⁷

• 6.02 x 10¹⁷

The d-electron configuration of Cr³⁺, Mn²⁺, Fe²⁺ and Ni²⁺ are 3d⁴, 3d⁵, 3d⁶ and 3d⁸ respectively. Which one of the following aqua complexes will exhibit the minimum paramagnetic behaviour?

(At. no. Cr = 24, Mn = 25, Fe = 26, Ni = 28)

• [Mn(H₂O)₆]²⁺

• [Fe(H₂O)₆]²⁺

• [Ni(H₂O)₆]²⁺

• [Ni(H₂O)₆]²⁺

Which of the following represents the correct order of the acidity in the given compounds?

• H₃CCOOH > BrCH₂COOH > ClCH₂COOH > FCH₂COOH

• FCH₂COOH > CH₃COOH >BrCH₂COOH > ClCH₂COOH

• BrCH₂COOH > ClCH₂COOH > FCH₂COOH >CH₃COOH

• BrCH₂COOH > ClCH₂COOH > FCH₂COOH >CH₃COOH

Which one of the following vitamins is water soluble? 

• vitamin - B

• vitamin - E

• vitamin - K

• vitamin - K

Which one of the following polymers is prepared by condensation polymerization? 

• Nylon - 66

• Teflon

• Rubber

• Rubber