Question

How many hours would it take for a $64g$ sample to decay to one-eighth of its original concentration? Given that the half life of radioactive sodium is $15.0$ hours.

• A. $3$
• B. $15$
• C. $30$
• D. $45$

Answer 1

The correct option is D $45$

$t=\frac{2.303}{k}$$log\frac{64}{8}$
$k=\frac{0.693}{15}=0.046$
$t=\frac{2.303}{0.046}$$log\frac{64}{8}=45$