In a moving coil galvanometer a radial magnetic field is obtained with concave magnetic poles, to have

Formula Used :

$\tau =$ $NIBA$

Detailed Solution:

In moving coil galvanometer a radial magnetic field is applied with concave magnetic poles, to have uniform magnetic field.
Since the magnified field is radial the plane of the coil is parallel to the magnetic field $\overrightarrow{\mathrm{B}}$ 

such that $\theta =90°$ and hence $\tau =$ $NIBA.$
The plane of coil is parallel to the field.

Hence, the correct option is B