A long cylindrical conductor with large cross section carries an...

For a long cylindrical conductor with uniform current distribution, apply Ampere's law to find the magnetic field.
At distance $r$ from the axis (inside the conductor, $r < R$): $B(r) = \frac{\mu_0 I r}{2\pi R^2}$ (proportional to $r$)
At the axis ($r = 0$): $B = 0$ (minimum)
At the surface ($r = R$): $B = \frac{\mu_0 I}{2\pi R}$ (maximum)
Analyzing the statements:
A. Maximum at ends and minimum at midpoint - FALSE. This describes behavior along the axis, but the magnetic field depends on radial distance, not axial position.
B. Maximum at the axis of the conductor - FALSE. The field is zero at the axis.
C. Minimum at the surface of the conductor - FALSE. The field is maximum at the surface.
D. Minimum at the axis of the conductor - TRUE. The field is zero at $r = 0$, making it the minimum.
E. Same at all points in the cross-section - FALSE. The field varies from 0 at the axis to maximum at the surface.
Only D is correct.