Question

Starting with a sample of pure $C{u}^{66}$,$\frac{7}{8}th$ of it decays into $Zn$ in $15mins$.The corresponding half-life is

• A. $10minutes$
• B. $15minutes$
• C. $5minutes$
• D. $7\frac{1}{2}minutes$

Answer 1

The correct option is C $5minutes$

Left amount of $Cu=1-\frac{7}{8}=\frac{1}{8}$
So,

Sample of $Cu$ decays into $\frac{1}{8}$ of original i.e $3$ half-lives
$\because 3$ half-lives $=15minutes$
$\therefore 1$ half-life $=5minutes$