A radioactive material has a half-life of 8 years. The activity of the material decreases to 1/8 of its original value in:

Correct Answer: (B) 24 years

The radioactive decay law states that the remaining activity is given by N = N₀(1/2)^n, where n is the number of half-lives. For activity to become 1/8 of original, (1/2)³ = 1/8, meaning 3 half-lives have passed. Thus, time elapsed = 3 × 8 years = 24 years.