What is the commercial name for calcium oxide?

We are asked to recall the commercial (trade) name of the compound calcium oxide, whose chemical formula is $$CaO$$.

First, let us remember how $$CaO$$ is obtained industrially. Limestone, which is nothing but calcium carbonate $$CaCO_3$$, is strongly heated in rotary kilns. During this calcination process the following reaction takes place:

$$CaCO_3 \rightarrow CaO + CO_2 \quad \text{(on heating)}$$

The freshly produced $$CaO$$ is a white, highly caustic solid that reacts vigorously with water. Because of the speed (quickness) with which it reacts and because it is obtained immediately after the decomposition of limestone, the material is popularly called “quick lime.”

Now, let us compare the given options with the above information:

A. “Quick lime” is the common name for $$CaO$$ as just discussed.

B. “Milk of lime” is not $$CaO$$; it is a milky suspension formed when $$Ca(OH)_2$$ (calcium hydroxide) is dispersed in water.

C. “Slaked lime” is the solid form of $$Ca(OH)_2$$ itself, obtained when water is added to quick lime: $$CaO + H_2O \rightarrow Ca(OH)_2$$. Hence slaked lime is calcium hydroxide, not calcium oxide.

D. “Limestone” is the mineral $$CaCO_3$$, the raw material from which $$CaO$$ is produced, so it is also different.

Only Option A matches $$CaO$$.

Hence, the correct answer is Option A.