d
Magnetic moment

\(M=i A\)

\(M=\left(\frac{q}{T}\right) \times \pi r^{2}=\frac{q \pi r^{2}}{\left(\frac{2 \pi r}{v}\right)}=\frac{q v r}{2}\)

\(M=\frac{q v}{2} \times \frac{v m}{q B}\)

\(M =\frac{ mv ^{2}}{2 B }\)

As we can see from the figure, direction of magnetic moment \((M)\) is opposite to magnetic field.

\(\overrightarrow{ M }=-\frac{ mv ^{2}}{2 B } \hat{ B }\)

\(=-\frac{m v^{2}}{2 B^{2}} \vec{B}\)