Constant current in a series wire Steps:

• Current I is defined as charge flow per unit time and remains constant along a single wire in steady state.
• Charge Q passing point R in time t gives I = Q/t.
• Since I is constant, the same I flows through point S.
• Thus, charge at S in time t is also I * t = Q.

Why A is correct:

• By the continuity equation for steady current, charge flow rate is uniform in a series conductor.

Why the others are wrong:

• B: Current flows through S, so charge is not zero.
• C: No halving occurs; current is unchanged by cross-section.
• D: No doubling; constant current means same charge flow.

Final answer: A