In Choose odd pair of words type of questions, certain pairs of words are given out of which the words in all the pairs except one, bear a certain common relationship. The candidate is required to decipher this relationship and chose the pair in which the words are differently related, as the answer.
(Volume : Litre), (Time : Second), (Length : Metre), (Resistance : Ohm), (Pressure : Barometer)
Clearly, the answer is (e).
In all other pairs, second is the unit to measure the first. On the other hand, barometer is an instrument.