Assertion: Molecular formula of water is ( H2O ).

Molecular formula is the representation of a composition of the molecule in a compound.

It is written in terms of the symbol of the elements in any molecule.

The molecular formula of water is ( H₂O ).

It means that one molecule of water will contain two atoms of hydrogen and one atom of oxygen.

Thus, option (A) is correct.

Hence, option (A) is correct i.e. both Assertion and Reason are correct and Reason is the correct explanation for Assertion