Which scales are used to measure temperatures?

Out of so many metals why mercury is used to measure the temperature in the thermometers?

Name a unit which can be used to measure very small mass.

Answer the following The absolute temperature (kelvin scale) T is related to the temperature T_C on the celsius scale by T_C = T - 273.15 . Why do we have 273.15 in this relation and not 273.16?