t₁/4 can be taken as the time taken for the concentration of a reactant to drop to 3/4 of its initial value. If the rate constant for a first order reaction is K, the t₁/4 can be written as

• 0.10 / K

• 0.29 / K

• 0.69 / K

• 0.69 / K

An amount of solid NH₄HS is placed in a flask already containing ammonia gas at a certain temperature and 0.50 atm. Pressure. Ammonium hydrogen sulphide decomposes to yield NH₃ and H₂S gases in the flask. When the decomposition reaction reaches equilibrium, the total pressure in the flask rises to 0.84 atm. The equilibrium constant for NH₄HS decomposition at this temperature is

• 0.30

• 0.18

• 0.17

• 0.17

In first order reaction, the concentration of the reactant decreases from 0.8 M to 0.4 M in 15 minutes. The time taken for the concentration to change from 0.1 M to 0.025 M is

• 30 minutes

• 60 minutes

• 7.5 minutes

• 7.5 minutes

The rate equation for the reaction 2A + B → C is found to be: rate k[A][B]. The correct statement in relation to this reaction is that the

• unit of K must be s^-1

• values of k is independent of the initial concentration of A and B

• rate of formation of C is twice the rate of disappearance of A

• rate of formation of C is twice the rate of disappearance of A

The soldiers of Napolean army while at Alps during freezing winter suffered a serious problem as regards to the tin buttons of their uniforms. White metallic tin buttons got converted to grey powder. This transformation is related to

• an interaction with nitrogen of the air at very low temperatures

• an interaction with water vapour contained in the humid air

• a change in the partial pressure of oxygen in the air

• a change in the partial pressure of oxygen in the air

Consider the following nuclear reactions


The number of neutrons in the element L is

• 142

• 164

• 144

• 144

The half-life of a radioisotope is four hours. If the initial mass of the isotope was 200 g, the mass remaining after 24 hours undecayed is

• 1.042 g

• 4.167 g

• 3.125 g

• 3.125 g

The compound formed in the positive test for nitrogen with the Lassaigne solution of an organic compound is

• Fe₄[Fe(CN)₆]₃

• Na₄[Fe(CN)₅NOS]

• Fe(CN)₃

• Fe(CN)₃

339.

At 518⁰C the rate of decomposition of a sample of gaseous acetaldehyde initially at a pressure of 363 Torr, was 1.00 Torr s^–1 when 5% had reacted and 0.5 Torr s^–1 when 33% had reacted. The order of the reaction is

• 0

• 2

• 3

• 1

An aqueous solution contains 0.10 M H₂S and 0.20 M HCl. If the equilibrium constants for the formation of HS– from H₂S is 1.0 x10^–7 and that of S^2- from HS^– ions is 1.2 x 10^–13 then the concentration of S^2- ions in aqueous solution is

• 5 x 10^-19

• 5 x 10-8

• 3 x 10^–20

• 6 x 10^-21