Ampere's Law, Cylinders, Solenoid & Toroid question from NEET 2019

Answer: (c)

1. Uniform current: inside $B = \frac{\mu_0 I d}{2\pi R^2} \propto d$.
2. Outside: $B = \frac{\mu_0 I}{2\pi d} \propto \frac{1}{d}$.
3. So the graph is a straight line up to $d = R$, then a $1/d$ fall: answer (c).