If $A$ and $B$ are two events such that $P(A|B) = P(B|A)$, and $A ∩ B ≠ \phi$ then

$P(A) = P(B)$

The correct answer is Option (2) → $P(A) = P(B)$

Given

$P(A|B)=P(B|A)$

Use conditional probability formulas:

$P(A|B)=\frac{P(A\cap B)}{P(B)}$

$P(B|A)=\frac{P(A\cap B)}{P(A)}$

Given equality:

$\frac{P(A\cap B)}{P(B)}=\frac{P(A\cap B)}{P(A)}$

Since $P(A\cap B)\ne0$, cancel it:

$\frac{1}{P(B)}=\frac{1}{P(A)}$

$P(A)=P(B)$