A solution of a substance ‘X’ is used for white washing.
Write the reaction of the substance ‘X’ named in given with water.

Hint: - Lime wash is pure slaked lime in water. It produces a unique surface glow due to the double refraction of calcite crystals. Limewash and whitewash both cure the same material. When whitewash or limewash is initially applied, it has very low opacity, which can lead novices to overthicken the paint.

Complete answer:
The chemical substance X which is used for whitewashing is Calcium oxide also known as quicklime or burnt lime or lime. The formula of substance X is CaO. It is a white or greyish white solid produced in large quantities by roasting calcium carbonate so as to drive off carbon dioxide. At room temperature, Calcium oxide will spontaneously absorb carbon dioxide from the atmosphere, reversing the reaction. It will also absorb water, converting itself into calcium hydroxide and releasing heat in the process. The bubbling that accompanies the reaction is the source of its name as “quick,” or living lime. The reaction of quicklime with water is sometimes used in portable heat sources. One of the oldest known products of a chemical reaction, quicklime is used extensively as a building material. It is sometimes used directly as a fertilizer, although calcium carbonate is usually preferred for that purpose.

Calcium oxide reacts vigorously with water to produce slaked lime (calcium hydroxide) releasing a large amount of heat.

$CaO(S)\; + \;{H_2}O(l) \to Ca{(OH)_2}(aq)$

Note: - Calcium oxide is an odourless, white to yellow, grey or brown granular powder. Its density is 3.34 g mL-1. The melting and boiling points are ${2613^ \circ }C$ and ${3850^ \circ }C$, respectively. It is soluble in water and reacts with water to form calcium hydroxide.