The hysteresis loop of a magnetic material has intercepts on the B...

The intercept on the $H$-axis of a hysteresis loop represents the coercivity of the material. Thus, the coercivity is $H_c = 2500$ A m$^{-1}$.

The magnetic intensity $H$ produced by the solenoid is given by $H = ni$, where $n$ is the number of turns per unit length and $i$ is the current.

Given:
$N = 100$
$L = 20$ cm $= 0.2$ m

The turn density is $n = \dfrac{N}{L} = \dfrac{100}{0.2} = 500$ m$^{-1}$.

To demagnetize the sample, the magnetic intensity must equal the coercivity:
$H = H_c$
$ni = 2500$
$500 \times i = 2500$
$i = 5$ A.

Answer: $5$