Half-life of substance A following first order kinetics is 5 days. Starting with 100g of A, the amount left after 15 days will be: 

1.  25 g 

2. 50 g 

3. 12.5 g 

4. 6.25 g 

If 'a' is the initial concentration of a substance that reacts according to zero-order kinetics and k is the rate constant, then the time for the reaction to go to completion is:
1. a/k
2. 2/ka
3. k/a
4. 2k/a

In a first order reaction, time required for completion of 99.9% is X times of half-life (t_1/2) of the reaction. When reaction is completed 99.9%, [R]_n = [R]₀ – 0.999[R]₀ .The value of X is-

1. 5
2. 10
3. 15
4. 20

The reaction of hydrogen and iodine monochloride is given as: 
H₂(g) + 2ICl(g) → 2HCl(g) + I₂(g) 
This reaction is of first order with respect to H₂(g) and ICl(g), for which of the following proposed mechanisms:
Mechanism A: 
H₂(g) + 2ICl(g) → 2HCl(g) + I₂(g) 
Mechanism B: 
H₂(g) + ICl(g) →HCl(g) + HI(g); slow 
HI(g) + ICl(g) →HCl(g) + I₂(g); fast

1. B Only

2. A and B both

3. Neither A nor B

4. A only

If 75 % of a first-order reaction was completed in 90 minutes, 60 % of the same reaction would be completed in approximately (in minutes):

(Take : log 2 = 0.30 ; log 2.5 = 0.40)

1. 50 min

2. 60 min

3. 70 min

4. 65 min

The correct graphical representation of first-order reaction is:

(a)		(b)
(c)		(d)

Consider the first-order gas-phase decomposition reaction given below.

A(g) → B(g) + C(g)

The initial pressure of the system before the decomposition of A was ${\mathrm{P}}_{\mathrm{i}}$. After the lapse of time t, the total pressure of the system increased by X units and became ${\mathrm{P}}_{\mathrm{t}}$. The rate constant k for the reaction is:

For a first-order reaction A → B the reaction rate at a reactant concentration of 0.01M is found to be $2.0\times {10}^{-5}\text{ mole }{\mathrm{L}}^{-1}{\mathrm{s}}^{-1}$. The half-life period of the reaction is: