Question

The half-life period of a radioactive substance is 70 days.one gram of the same substance will remain 0.25g after how many days? A. 70days B. 140days C. 210 days D. 280days

Answer 1

solution :-

$\sf{N(t)=N_0(\dfrac{1}{2})^\dfrac{t}{t_1/2}}$

Here,

N(t) = quantity of the substance remaining

$\sf{N_0}$ = intial quantity of the substance

t = time elapsed

t(1/2) = half life of the substance

The formula of half life period was introduced by Rutherford.

Half life of some isotopes :-

oxygen 16 = infinite

carbon 14 = 5730 years

cobalt 60 = 527 years

silver 94 = 42 seconds

uranium 238 = 4460000000 years