Relations in Drift Current Derivation Steps:

• Current I equals total charge passing a cross-section per unit time.
• In time t, drifting electrons cover distance vt, forming a cylindrical volume of length vt and area A.
• Charge passing equals (electrons in that volume) times q, divided by t to get I.
• Simplifying yields I = nAvq, using charge-time, distance-speed-time, and volume-length-area relations.

Why C is correct:

• The derivation relies on electron flux rate (nAv electrons per second) times q, not total number of electrons in a static volume.

Why the others are wrong:

• A is used: Total charge Q = It, so I = Q/t.
• B is used: Drift length = vt for the segment of electrons passing in time t.
• D is used: Effective volume = A × (vt) containing passing electrons.

Final answer: C