Correct option is B
Given: Coal : Fuel
Coal : Fuel represents a category and subcategory relationship, where coal is a type of fuel.
Analyzing the Options
Option (a): Zoo : Animal
A zoo is a place where animals are kept, not a type of animal (Incorrect)
Option (a): Ant : Insect
An ant is a type of insect, just as coal is a type of fuel (Correct)
Option (a): Hen : Egg
A hen lays eggs, but an egg is not a type of hen (Incorrect)
Option (a): Mammal : Cow
A cow is a type of mammal, which is the reverse of the given pair (Coal is a type of Fuel, not Fuel is a type of Coal (Incorrect)
Thus, the correct option is (B) Ant : Insect.