MCQs on Half-Life

Half-Life tells about the rate of decay of any radioactive substance. It is the time required for the decay of half of the atomic nuclei of a radioactive substance from its initial value. It is independent of the amount of the radioactive element. Irrespective of the amount present at a time, it will always be halved after one half-life period.

1. 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

2. 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

3. 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

4. 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

5. 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

6. 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

7. What would be the remaining concentration of 10.4 micrograms of ²³¹Pa after 3.25 x 10⁵ years if the half-life is 3.25 x 10⁴ years?

(a) 0.0240 micrograms

(b) 2.18 micrograms

(c) 1.4 micrograms

(d) 0.0102 micrograms

8. 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

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

(a) 4.5 x 10⁹ years

(b) 9 x 10¹⁰ years

(c) 4.5 x 10¹⁰ years

(d) 9 x 10⁹ years

10. Which of the following radiations is the most penetrating?

(a) 𝞬

(b) 𝜶

(c) 𝜷

(d) neutron

Answer