Half Life MCQs

Half-Life describes the rate at which a radioactive substance decays. It represents the time needed for half of the atomic nuclei in a sample to decay from their original quantity. This period is constant and does not depend on the amount of the radioactive material present. Regardless of the initial quantity, the substance will always be reduced by half after each half-life period.

How many milligrams of tritium will remain after 49.2 years if the starting amount is 32 mg? The half-life of tritium is 12.3 years.

(a) 8 mg
(b) 2 mg
(c) 1 mg
(d) 4 mg

What would be the remaining concentration of 10.4 micrograms of²³¹Pa after 3.25 x 10⁵years if the half-life is 3.25 x 10⁴years?

(a) 0.0240 micrograms
(b) 2.18 micrograms
(c) 1.4 micrograms
(d) 0.0102 micrograms

If a body requires 0.01 m activity of radioactive substance (half-life = 6 hrs) after 24 hrs of injection then what is the maximum activity of injection to be injected?

(a) 0.04
(b) 0.32
(c) 0.16
(d) 0.08

What would be the remaining concentration of 300 g of radioactive substance after 18 hours if the half-life is 3 hours?

(a) 9.37 g
(b) 2.34 g
(c) 3.34 g
(d) 4.68 g

Uranium-238 forms thorium-234 after radioactive decay and has a half-life of 4.5 x 10⁹years. How many years will it take to decay 75% of the initial amount?

(a) 4.5 x 10⁹years
(b) 9 x 10¹⁰years
(c) 4.5 x 10¹⁰years
(d) 9 x 10⁹years

200 mg of 14C will become 25 mg in how many years if the half-life is 5760 years?

(a) 5760 years
(b) 17280 years
(c) 23040 years
(d) 11520 years

The radioactive isotope of phosphorus, P-32 is used as a tracer in the liver. If 3.5 mg is left in a sample after 288 hrs then how much P-32 was administered initially? [Half-life of P-32 is 14.3 days]

(a) 7 mg
(b) 6.26 mg
(c) 1.96 mg
(d) 4.17 mg

What would be the remaining concentration of 1 g of radioactive substance after 400 days if the half-life is 100 days?

(a) 1/16
(b) 1/4
(c) 1/2
(d) 1/8

Find the half-life of 614C if 𝝺 is 2.31 x 10^-4.

(a) 4 x 10³ years
(b) 3 x 10³ years
(c) 3.5 x 10⁴ years
(d) 2 x 10² years

Which of the following radiations is the most penetrating?

(a) 𝞬
(b) 𝜶
(c) 𝜷
(d) neutron