The quantity of heat required to change the temperature of 1 kg of a substance by $1^{\circ }C$ is called its:

The correct option is A Specific heat
We know that , heat $Q=mC\Delta T$ where $m=$ mass of the body, $C=$ specific heat and $\Delta T=$ change in temperature.

Thus, $C=\frac{Q}{m\Delta T}$

So when $m=1kg$ and $\Delta T=1^{o}C$, $C=Q$

The required heat is the specific heat.