Which of the following materials can be used for the inlet thimble of a masonry chimney?

The use of fireclay for the inlet thimble of a masonry chimney is appropriate for several reasons. Fireclay is a ceramic material that can withstand high temperatures and is specifically designed for use in environments exposed to significant heat, which is common in chimney applications. Its resistance to thermal shock and excellent durability makes it suitable for the conditions within a chimney where combustion gases are vented. Fireclay is also non-combustible, thus ensuring safety and compliance with building codes related to fire hazards.

In contrast, the other materials listed are unsuitable for this application. Plastic, for instance, can melt or deform under high temperatures, presenting a fire risk. Wood is combustible and would easily ignite in the presence of high heat, making it dangerous in a chimney environment. Glass, while able to withstand heat to some extent, could shatter under the thermal stresses involved and is not structurally sound enough to serve as a chimney component. Therefore, fireclay is the only appropriate choice for the inlet thimble of a masonry chimney due to its properties that ensure safety and efficacy.