What happens when limestone is heated

It breaks into calcium oxide and carbon di oxide.

Limestone; When used to form lime, a sedimentary rock is composed of calcium carbonate salts. The other name of limestone is limestone. In the structure of at least 90% CaCO3 (calcium carbonate) is called the principal limestone rocks. Limestone, cement used in construction.

The most plausible answer is b, duration. the given amount of time is considered how long it last for.