Words given on the left side of (::) are related with each other by some Logic/Rule/Relation. Select the missing word/ word pair on the right side of (::) from the given alternatives based on the same Logic/Rule/Relation.

Watt  :  Power  ::  Ohm  :  ?

Electrical Resistance 

In this analogy, the relationship between the words on the left side (::) and the words on the right side (::) involves a unit of measurement and its corresponding physical property or concept.

Watt is a unit of measurement for power. Similarly, Ohm is a unit of measurement for Electrical Resistance.

So, the missing word is Electrical Resistance.