Question

The decay constant, for a given radioactive sample is $0.3465day^{- 1}$ what percentage of this sample will get decayed in a period of 4 days?

• A. 100%
• B. 50 %
• C. 75%
• D. 10%

Answer 1

Answer: (C)

75%

Answer 2

: here, $\lambda = 0.3465day^{- 1}$

$t = 4days$

$T_{12} = \frac{0.693}{\lambda} = \frac{0.693}{0.3465} = 2days$

$\therefore n = \frac{t}{T_{1/2}} = \frac{4}{2} = 2$

Hence sample left un decayed after a period of 4 days

$\frac{N}{N_{0}} = \left( \frac{1}{2} \right)^{2} = \left( \frac{1}{4} \right) = 25\%$

$\therefore$Sample decayed = 75%