Question

The half life of a radioactive isotope is three hours. If the initial mass of the isotope were $256$ $g$, the mass of it remaining undecayed after $18$ hours would be:

• A. $4$ $g$
• B. $8$ $g$
• C. $12$ $g$
• D. $16$ $g$

Answer 1

Answer: (A)

$4$ $g$

$t=\frac{2.303\times t_{1/2}}{0.693}\times log\frac{Ao}{A}$

$18=\frac{2.303\times 3}{0.693}\times log\frac{256}{A}$

$A=4g$