Discussion
Assertion: a cell's EMF can be measured accurately with an ordinary low resistance voltmeter. Reason: the EMF is the potential difference between the electrodes.
Answer: C
Correct answer: the assertion is false although the reason offered is a true statement in itself
The reason is a true description of what EMF is, but the assertion fails on the method. A low resistance voltmeter draws appreciable current, and drawing current polarises the electrodes and produces a drop across the internal resistance, so the reading falls below the true EMF. The measurement must be made at essentially zero current - by a potentiometer, or by a modern electrometer of very high input impedance.
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