Why is water used as a coolant?

Which of the following statements is $NOT$ true?

Two substances $A$ and $B$ of the same mass are heated at a constant rate. The variation of temperature $\theta$ of the substances with time $t$ is shown in the figure. Choose the correct statement.

$500 \ g$ of water is heated from $30^{\circ}C$ to $90^{\circ}C$. What is the change in its internal energy? (Specific heat of water is $4184 \ J \ kg^{-1} \ K^{-1}$)

$A$ small electric heater is used to heat $200 \,g$ of water. The time required to bring all this water from $40^{\circ} C$ to $100^{\circ} C$ is $200 \,s$. If the specific heat of the water is $4200 \,J \,kg^{-1} \,K^{-1}$, then the power supplied by the heater is: (in $\,W$)

The specific heat $C$ of a solid at low temperature shows temperature dependence according to the relation $C = D T^{3}$,where $D$ is a constant and $T$ is the temperature in Kelvin. $A$ piece of this solid of mass $m \ kg$ is taken and its temperature is raised from $20 \ K$ to $30 \ K$. The amount of heat required in the process in energy units is