Two separate defects sit inside the assertion, and either one of them is enough to sink it. The reason, on the other hand, is a clean restatement of Section 34 of the Penal Code. Work through them in that order.
Defect one is the section number. Section 341 punishes wrongful restraint, an offence of stopping a person from going where he has a right to go. Nobody is convicted of murder under it. The punishment there runs to one month of simple imprisonment or a fine of five hundred rupees. Murder attracts Section 302, and the definition sits in Section 300.
Defect two is the reasoning about joint liability. The facts say X and Y entertained the idea independently. Common intention under Section 34 is not two people happening to want the same thing. It requires a pre-arranged plan and a shared mind before the criminal act. Where the plan is missing, each man stands or falls on his own act alone. If X's wound killed Z, X faces murder; if it did not, his liability is only for what his own blow amounted to. Y is judged the same way, and neither carries the other's act.
The reason itself is unimpeachable. Section 34 reads that when a criminal act is done by several persons in furtherance of the common intention of all, each of them is liable for that act in the same manner as if it were done by him alone.
Let's summarize:
So the assertion is false, the reason is true, and option (D) is the answer.