Calcium Oxide is commonly known as Which one of the following substance hygroscopic in nature?

Here are the solutions to the questions:

11. Calcium Oxide is commonly known as

Calcium oxide ($\text{CaO}$) is a chemical compound widely known by its common name, quicklime.

The correct option is D.
$\boxed{\text{D}}$

12. Which one of the following substance hygroscopic in nature?

A hygroscopic substance readily absorbs moisture from the atmosphere.

• A. $\text{CaCl}_2$ (Calcium chloride) is a highly hygroscopic substance, often used as a desiccant.
• B. $\text{CuO}$ (Copper(II) oxide) is not typically considered hygroscopic.
• C. $\text{MgCl}_2$ (Magnesium chloride) is also hygroscopic