A first order reaction has a specific reaction rate of 10^$$-$$2 sec^$$-$$1. How much time will it take for 20 g of the reactant to reduce to 5 g?

Mechanism of a hypothetical reaction
X₂ + Y₂ $$ \to $$ 2XY, is given below :
(i)   X₂ $$ \to $$ X + X (fast)
(ii)  X + Y₂ $$\rightleftharpoons$$ XY + Y (slow)
(iii) X + Y $$ \to $$ XY (fast)
The overall order of the reaction will be

The decomposition of phosphine (PH₃) on tungsten at low pressure is a first-order reaction. It is because the

The rate of first-order reaction is 0.04 mol L^$$-$$1 s^$$-$$1 at 10 seconds and 0.03 mol L^$$-$$1 s^$$-$$1 at 20 seconds after initiation of the reaction. The half-life period of the reaction is