21        B

Option A: Would have been correct for “P.d. across the internal resistance of a cell”.

Option B: Correct.

Option C: Would have been correct if “total energy dissipated in it over a period of time” is replaced by “Rate of energy dissipation in the resistor (power)”.

Option D: The statement is a bit vague and unconventional but it is not totally wrong actually. Energy is converted from electrical to non-electrical in the cell due to the internal resistance of the cell. Perhaps would be more correct if “to move a unit charge” is replaced by “per unit charge moving”.

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