Can every solid be changed into a liquid?

Answer 1

The phase, whether solid, liquid, or gas, of any substance depends upon two factors, temperature and pressure. There is a temperature and pressure at which any solid will melt and become a liquid. The great majority of solids can be melted by heating them at normal air pressure, but not all solids. Frozen carbon dioxide, for example (also known as dry ice) goes directly from the solid phase to the gas phase at normal air pressure, without ever being a liquid, as it is heated. However, with a higher pressure it can be made into a liquid.