This problem asks a single practical question: does a man lose his right to defend himself just because the person attacking him is insane? The Penal Code answers that with Section 98, and once that section is on the table the assertion and the reason fit together neatly.
Two provisions are working side by side here. Section 84 shields X, because a person of unsound mind who does not know the nature of his act commits no crime. Section 98 shields Y, because the right of private defence is measured by the danger, not by the attacker's capacity to be punished. Both men walk away without liability, which is exactly what the Code intends.
Let's summarize:
So both statements are true and the reason correctly explains the assertion. Option (A) is the answer.