Explanation

(d) $\mu_{r} = 1 + \frac{I}{H};$ as we know $I$ dependent on $H$, initially value of $\frac{1}{H}$ is small so value of $\mu_{r}$ increases with $H$ but slowly. With further increase of $H$, value of $\frac{1}{H}$ also increases, $i.e.,\mu_{r}$ increases speedily. When material is fully magnetized $I$ becomes constant, then with the increase of $H\left\lbrack \frac{1}{H}\ decreases \right\rbrack\mu_{r}$ decreases. This is in accordance with the option (d)