QJEEAdv78Che117: JEE Advanced 1978 Chemistry - Class 11 JEEAdv78Che117 Solution: The substance absorbs CO 2 and violently reacts with water. The …

The correct answer to the question is Option B: CaO.

Let's break down the reasoning:

CaO (Calcium oxide), also known as quicklime, vigorously reacts with water to form calcium hydroxide (Ca(OH)₂) and releases a significant amount of heat. This reaction is known as slaking of lime and can be represented as:

$\text{CaO} + \text{H}_2\text{O} \rightarrow \text{Ca(OH)}_2$

Additionally, calcium oxide has a strong affinity for carbon dioxide (CO₂). It absorbs CO₂ from the air to form calcium carbonate (CaCO₃) through the following reaction:

$\text{CaO} + \text{CO}_2 \rightarrow \text{CaCO}_3$

Thus, CaO fulfills both conditions: it absorbs CO₂ and reacts violently with water. The other substances listed do not meet these criteria:

CaCO₃: Calcium carbonate reacts with acids but does not react violently with water and does not absorb CO₂.

H₂SO₄: Sulfuric acid is a liquid that reacts vigorously with water (specifically, dilution of concentrated sulfuric acid is exothermic), but it does not absorb CO₂.

ZnO: Zinc oxide is an amphoteric oxide that does not react violently with water and does not absorb CO₂.

Therefore, the most appropriate answer is:

Option B: CaO