Temperature of water at the surface of a lake is $ -20^{\circ}C$. Then,the temperature of water just below the lower surface of the ice layer is ...... $^{\circ}C$.

The surface of the lake is at $2^{\circ}C$. Find the temperature of the bottom of the lake in $^{\circ}C$.

$A$ constant pressure air thermometer gave a reading of $47.5$ units of volume when immersed in ice cold water, and $67$ units in a boiling liquid. The boiling point of the liquid will be .......... $^\circ C$.

$A$ thermometer graduated according to a linear scale reads a value $x_0$ when in contact with boiling water,and $x_0/3$ when in contact with ice. What is the temperature of an object in ${}^oC$,if this thermometer in contact with the object reads $x_0/2$?

Maximum density of $H_2O$ is at temperature

The study of physical phenomena at low temperatures (below liquid nitrogen temperature) is called: