When impurities are added to a substance, it would lower its freezing point.
Impurities are other foreign substances.
Example:
I have 2 cups of water, A and B.
I add salt to B. When I try to freeze the water in both cups, A would freeze at 0oC but B would freeze maybe at –10oC.
This means B would stay as a liquid even at 0oC or -2oC or lower until the temperature reaches –10oC.
When A becomes solid ice at 0oC, B is still liquid.

Melting point of ice is lowered by an increase in pressure and is increased by a drop in pressure.

At higher pressure, an ice cube would melt at temperatures lower than 0oC.

At lower pressure (on the mountain), ice would only melt at temperatures higher than 0oC. Which is why there can be snow on the mountain top even when surrounding temperatures are above 0oC.

Boiling is a change of state from liquid to gas.
Boiling occurs at a fixed temperature. During boiling, temperature remains constant.
This temperature is known as the boiling point of the substance.
Heat is taken in / absorbed during this process.
Liquid will remain at boiling point until all the liquid has changed to gas.
(phenomena is pretty similar to melting)

The reverse of boiling is condensation.

It is the process of change from gas to liquid.
It occurs at a fixed temperature which is the boiling point of the substance.
Heat is given off during this process.

The thermal energy that is absorbed or released; causing a change in state is known as latent heat.

For melting or freezing, it is known as latent heat of fusion, Lf.
For boiling or condensation, it is known as latent heat of vaporisation, Lv

Unit for both Lf, Lv is joule or J

Adding impurities will raise the boiling point of an object.
That means to say the liquid will now boil at a higher temperature.

Lower pressure would lower the boiling point of water.
Water will boil very quickly on the mountain top but the temperature reached is lower than 100oC.

Increasing pressure would raise the boiling point of water.
Water will boil at a higher temperature above 100oC

Evaporation is the change of state from liquid to gas at any temperature.

cora.