Calculate the time required to lose radioactive intensity of a radioactive sample of `""^(24)Na` to 70% of its original value. Given `t_(0.5)` of `""^(24)Na = 14.8` hours.

Options

A. 20.5 hrs.
B. 25.7 hrs .
C. 28.8 hrs
D. 27.6 hrs.

Answer

B

Explanation

`lambda = (0.693)/(t_(0.5)) = (0.693)/(14.8) = 4.68 xx 10^(-2)hr^(-1), " "t = (2.303)/(lambda) log "" (N_(0))/(N) = (2.303)/(4.68 xx 10^(-2)) log "" (100)/(30) = 25.73` hrs