The half-life of a radioactive element is 10 h. How much will be left after 4 h in 1 g atom sample?

• 45.6 x 10²³ atom

• 4.56 x 10²³ atom

• 4.56 x 10²¹ atom

• 4.56 10²⁰ atom

Radioactivity of a sample (Z = 22) decreases 90% after 10 yr. What will be the half-life of the sample? 

• 5 yr

• 2 yr

• 3 yr

• 10 yr

In the reaction 3A → 2B, rate of reaction $+\frac{\mathrm{d}\left(\mathrm{B}\right)}{\mathrm{dt}}$ is equal to

• $-\frac{1}{3}\frac{\mathrm{d}\left[\mathrm{A}\right]}{\mathrm{dt}}$

• $-\frac{2}{3}\frac{\mathrm{d}\left[\mathrm{A}\right]}{\mathrm{dt}}$

• $+\frac{2\mathrm{d}\left[\mathrm{A}\right]}{\mathrm{dt}}$

• $-\frac{3}{2}\frac{\mathrm{d}\left[\mathrm{A}\right]}{\mathrm{dt}}$

If the volume of the vessel in which the reaction

2NO + O₂ → 2NO₂

is occurring is diminished to 1/3rd of its initial volume. The rate of the reaction will be increased by

• 3 times

• 9 times

• 27 times 

• 36 times

715.

The half-life period of radioactive element is 140 days. After 560 days, 1 gram of element will reduce to

• 1/2 g

• 1/4g

• 1/8 g

• 1/16g

In a chemical reaction two reactants takes part. The rate of reaction is directly proportional to the concentration of one of them and inversely proportional to the concentration of the other. The order of reaction is :

• 0

• 1

• 2

• 4

If the rate constant for a first order reaction is k, the time (t) required for the completion of 99% of the reaction is given by:

• t = 6.909/k

• t = 4.606/k

• t = 2.303/k

• t = 0.693/k