Question

which of the following is secreted around an irritant to make a pearl in certain molluscs? sea water nacre sand chitin

Explanation:

When an irritant enters certain molluscs, they secrete nacre (also known as mother - of - pearl) around it layer by layer to form a pearl. Sea water is the environment, sand can be an irritant, and chitin is not related to pearl - formation in this context.

Answer:

nacre