A moving coil galvanometer has 100 turns and each turn has an area...

Torque produced in a moving coil galvanometer is, $τ = BINAsinϕ$.

Let torsional constant of the suspension wire be $C$, then $C\theta = BINAsin90 °$

$⇒ C = \dfrac{BINA}{\theta} = \dfrac{0 . 01 \times 10 \times {10}^{- 3} \times 100 \times 2 \times {10}^{- 4}}{0 . 05}$

$= 4 \times {10}^{- 5}N - m / rad .$

Therefore, $x = 4$.