Quick lime is:
A.\[{\text{Ca}}{\left( {{\text{HC}}{{\text{O}}_3}} \right)_2}\]
B.\[{\text{CaC}}{{\text{O}}_3}\]
C.\[{\text{Ca}}{\left( {{\text{OH}}} \right)_2}\]
D.\[{\text{CaO}}\]

:Hint:Quick lime is produced by heating calcium carbonate at high temperature and quicklime produces slaked lime when treated with water. Molar mass of quick lime is \[56{\text{gmo}}{{\text{l}}^{ - 1}}\] .

Complete step by step answer:
Calcium oxide is also known as quick lime. The chemical formula of quick lime or calcium oxide is \[{\text{CaO}}\] . It can be prepared by heating calcium carbonate \[{\text{CaC}}{{\text{O}}_3}\] at high temperature \[{800^o}{\text{C}}\] . This reaction is as follow: \[{\text{CaC}}{{\text{O}}_3}\overset {{{800}^o}{\text{C}}} \leftrightarrows {\text{CaO}} + {\text{C}}{{\text{O}}_2}\] . When quick lime is added to water it produces calcium hydroxide and paste of calcium hydroxide in water is known as milk of lime. Quick lime has basic nature. Reaction of quick lime with carbon at very high temperature produces calcium carbide. Quick lime is used in manufacture of bleaching powder, cement, glass, calcium carbide , purification of sugar, as a drying agent for ammonia and ethanol, as basic lining in furnaces, for making soda lime.
Calcium hydroxide is also known as slaked lime. \[{\text{Ca}}{\left( {{\text{OH}}} \right)_2}\] is the chemical formula of slaked lime or calcium hydroxide. On passing carbon dioxide to slaked lime, solution turns milky as: \[{\text{Ca}}{\left( {{\text{OH}}} \right)_2} + {\text{C}}{{\text{O}}_2} \to {\text{CaC}}{{\text{O}}_3} + {{\text{H}}_2}{\text{O}}\] and on reaction of chlorine with slaked lime produces bleaching powder as follow: \[{\text{Ca}}{\left( {{\text{OH}}} \right)_2} + {\text{C}}{{\text{l}}_2} \to {\text{CaOC}}{{\text{l}}_2} + {{\text{H}}_2}{\text{O}}\] . Slaked lime is used for softening of hard water, for purification of sugar, in manufacture of bleaching powder, caustic soda, soda lime, preparation of mortar and pestle.
Calcium carbonate is also known as limestone. \[{\text{CaC}}{{\text{O}}_3}\] is a chemical formula of limestone or calcium carbonate. It is found in rocks, pearls, shells, eggs, etc. It is a white colored and odorless compound. It is mainly used in construction industry, preparation of cement, purification of iron, oil industries, as disinfectant agent, as chalk for teaching purposes, etc.

Thus, the correct option is D.

Note:
\[{\text{Ca}}{\left( {{\text{HC}}{{\text{O}}_3}} \right)_2}\] is known as calcium hydrogen carbonate. It is also known as cleansing lime. Soda lime is a mixture of sodium hydroxide and slaked lime or calcium hydroxide.