Question

Assertion :The magnetic moment ($\mu$) of an electron revolving around the nucleus decreases with increasing principle quantum number ($n$). Reason: Magnetic moment of the revolving electron $\mu \propto n$

• A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
• B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
• C. Assertion is correct but Reason is incorrect
• D. Assertion is incorrect but Reason is correct

Answer 1

The correct option is D Assertion is incorrect but Reason is correct

Current due to revolving electron is expressed as: $i=\frac{e}{2\pi r/v}$ $=\frac{ev}{2\pi r}$

Hence, magnetic moment due to this electron $=iA=\frac{ev}{2\pi r}\pi r^2$ $=\frac{evr}{2}$

The radius of $n^{th}$ orbit is proportional to $n^2$.

The velocity of electron in $n^{th}$ orbit is proportional to $\frac{1}{n}$.

Hence, the magnetic moment $\mu$ is proportional to $n$

Hence, Assertion is incorrect, but Reason is correct.