Half-life of a radioactive substance is `12.5 h` and its mass is `256 g`. After what time the amount of remaining substance is `1g`?

Options

A. 100h
B. 75h
C. 150h
D. 125h

Answer

A

Explanation

Number of atoms is proportional to mass of the substance
using `N/N_0 = (1/2)^n , " we have " 1/256 = (1/2)^n`
`therefore (1/2)^8 = (1/2)^n therefore n=8`
`therefore n = t/T therefore t = nt = 8xx 12.5 = 100 h`