d
From figure
$\sin ^{\prime} \frac{\theta}{2}=\frac{x}{r}$
$\Rightarrow x=r(\sin ) \frac{\theta}{2}$
Hence, new magnetic moment
$M^{\prime}=m(2 x)=m \cdot 2 r \sin ^{\prime} \frac{\theta}{2}$
$=m \cdot \frac{2 l}{\theta} \sin \frac{\theta}{2}=\frac{2 m l \sin ^{\prime} \theta / 2}{\theta}$
$\frac{2 M \sin (\pi / 6)}{\pi / 3}=\frac{3 M}{\pi}$