Option A is the correct answer.
Before doing this question we should know the following points.
- Number of equivalence classes = Number of states in Minimal FA (MFA)
- In MFA, we get some language at each and every stage. These languages are mutually exclusive and are called equivalence classes.
So to solve this question, first convert the given Right Linear Regular Grammar into DFA.
There are two states named $S$ and $A$.
The language at state $S$ represents one Equivalence Class. $\Bigl \{ w \in (a + b)^* \mid \text{ #a(w) is even} \Bigr \}$
The language at State $A$ represents another Equivalence Class. $\Bigl \{ w \in (a + b)^* \mid \text{ #a(w) is odd} \Bigr \}$