Question

Half-life of ${}^{221}Fr$ is 4.8 min. If 1 mg of the isotope is isolated, how much will remain after 19.2 min?

• A. 0.0625 mg
• B. 0.0525 mg
• C. 0.0725 mg
• D. None of these

Answer 1

Answer: (A)

0.0625 mg

Given that

Half-life = 4.8 min.
Time = 19.2 min
Now,

Number of half-life, n $=\frac{time}{halflife}=\frac{19.2}{4.8}=4$

$\therefore C=C_o{\left(\frac{1}{2}\right)}^y$

$=1mg{\left(\frac{1}{2}\right)}^4$

$=\frac{1}{16}mg$

$=0.0625mg$