'A' is a peon of a store room filled with wheat. 'B' is the owner of the store room. 'A' introduces water into the store so that wheat be destroyed. 'A' has committed the offence of

The act described in the question constitutes the offence of Mischief as defined under Section 425 of the Indian Penal Code (IPC). According to this section, whoever with intent to cause, or knowing that he is likely to cause, wrongful loss or damage to any person, causes the destruction of any property or any change in it that diminishes its value or utility, commits mischief.

This specific scenario is directly derived from Illustration (b) of Section 425, which states: "A introduces water into an ice-house belonging to Z and thus causes the ice to melt, intending wrongful loss to Z. A has committed mischief." Similarly, 'A' introducing water to destroy 'B's wheat is an act of mischief. Cheating requires deception, and Criminal Breach of Trust requires dishonest misappropriation of property, whereas the primary intent here is the destruction of property.