A radioactive substance has half-life T. The time required for 7/8 of the original mass to disintegrate is:
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Question

A radioactive substance has half-life T. The time required for 7/8 of the original mass to disintegrate is:

G1 Physics · Accepted Answer

If 7/8 disintegrates, the remaining fraction is 1 − 7/8 = 1/8 After n half-lives, N/N₀ = (1/2)ⁿ So, (1/2)ⁿ = 1/8 = (1/2)³ Hence n = 3. Required time = 3T. Option C follows.