When limestone is heated around 1270 K we get:

The correct option is C Quick lime and carbon dioxide
The process of converting limestone to quicklime involves heating limestone to a temperature of 1070-1270 K. This thermal dissociation reaction produces carbon dioxide $\left(C{O}_2\right).$
$CaC{O}_3\stackrel{\Delta }{\rightleftharpoons }CaO+C{O}_2$
$C{O}_2$ is removed as soon as it is produced to enable the reaction to proceed to completion.

Theory
Calcium Oxide or quick lime (CaO):
Properties:
It is a white amorphous solid with a melting point of 2870 K.
On exposure to the atmosphere, it absorbs moisture and $C{O}_2$.
$CaO+H_{2}O\to Ca(OH{)}_2$
$CaO+C{O}_2\to CaC{O}_3$
The addition of a limited amount of water breaks the lump of lime. This is called slaking of lime.
It combines with acidic oxides at high temperatures.
$CaO+Si{O}_2\to CaSi{O}_3$
$6CaO+P_4{O}_{1}0\to 2C{a}_3(P{O}_4{)}_2$
Preparation:
It can be obtained by heating CaCO3 at 1070 – 1270 K.
$CaC{O}_3\stackrel{\text{heat}}{\rightleftharpoons }CaO+C{O}_2$
$C{O}_2$ is removed as soon as it is produced to enable the reaction to proceed to completion.
Uses:
An important primary material for manufacturing cement.
In the manufacture of $N{a}_{2}C{O}_3$ from caustic soda.
In the purification of sugar and manufacture of dyestuff.