A steady current flows in a metallic conductor of non-uniform cross-section. The quantity that is constant along the length is

Current only

The correct answer is Option (4) → Current only

Explanation:

For a conductor of non-uniform cross-section, the current $I$ remains constant throughout because of the principle of conservation of charge.

However, the drift speed $v_d$ and the electric field $E$ vary along the conductor since they depend on the cross-sectional area $A$ as

$ I = n e A v_d $

Thus, when $A$ changes, $v_d$ and $E$ change, but $I$ remains constant.