A radioactive substance has a half life of 5 days. After 20 days it was foundd the `3 g` of the isotope left in the container. The initial weight of the isotope was
`a `48 g` b. `36 g` c. `18 g` d. `24 g`

Options

A. `a `48 g`
B. b. `36 g`
C. c. `18 g`
D. d. `24 g`

Answer

`a `48 g`

Explanation

`t_(1//2) = 5 "days", T = 20 "days"`
we know `T = nt_(1//2)`
`:.n = (T)/(t_(1//2)) = (20)/(5) = 4`
`N = ((1)/(2))^(n) N_(0)`
`:. N_(0) = N xx (2)^(4) = 3 xx (2)^(4) = 48 g`