What is the half-life of a 12 g sample of radioisotope that decayed to 6 g in 28 years?
A. 28 years
B. 14 years
C. 56 years
D. 7 years

A. 28 years

Explanation:

Applying,

R = R'(2ᵃ/ⁿ) Equation 1

Where R = Original sample, R' = Sample left after decay, a = Total time taken to decay, n = half life.

From the question,

Given: R = 12 g, R' = 6 g, a = 28 years.

Substitute into equation 1 and solve for n

12 = 6(2²⁸/ⁿ)

12/6 = 2²⁸/ⁿ

2²⁸/ⁿ = 2

Equation the base,

28/n = 1

n = 28 years.

Hence the half-life is 28 years

they are all solids.