Question

The ratio of the time periods taken by electron in $2^{nd}$ and $5^{th}$ orbits of $L{i}^{2+}$ is

• A. $4:25$
• B. $8:125$
• C. $8:25$
• D. $4:125$

Answer 1

The correct option is B $8:125$

Period of revolution $\propto \frac{n^3}{Z^3}$
$Z=2$

The ratio of the time period of taken by electron in $1^{st}$ and $3^{rd}$ orbits of $L{i}^{2+}$ = $\frac{2^3}{3^3}:\frac{5^3}{3^3}=8:125$