Question

The half life of $Sr$ is $28$ years. The fraction of the specimen that remains undecayed after $40$ years will be

• A. $21$ %
• B. $37$ %
• C. $45$ %
• D. $63$ %

Answer 1

Answer: (B)

$37$ %

Here decay constant is $\lambda =0.693/28peryear$

The fraction of the specimen that remains undecayed after $40$ years will be

$exp(-\lambda \times 40)=exp(-0.99)=0.3716=37.16\%$