Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R:
Assertion A: The H-O-H bond angle in water molecule is 104.5°.
Reason R: The lone pair - lone pair repulsion of electrons is higher than the bond pair - bond pair repulsion.

The water molecule has two lone pairs on the central oxygen atom and two bond pairs (O-H bonds). According to VSEPR theory, the electron geometry around oxygen is tetrahedral.

In a perfect tetrahedral arrangement, the bond angle would be $$109.5°$$. However, the lone pair-lone pair repulsion is greater than lone pair-bond pair repulsion, which in turn is greater than bond pair-bond pair repulsion. The two lone pairs on oxygen push the bonding pairs closer together, reducing the H-O-H bond angle from the ideal $$109.5°$$ to $$104.5°$$.

Therefore, Assertion A is true — the H-O-H bond angle in water is indeed $$104.5°$$. Reason R is also true — lone pair-lone pair repulsion is higher than bond pair-bond pair repulsion. Moreover, R correctly explains A, because it is precisely this stronger lone pair repulsion that compresses the bond angle from $$109.5°$$ to $$104.5°$$.

The correct answer is Option (4): Both A and R are true, and R is the correct explanation of A.