What happens to the temperature of a substance while it boils? (Does it increase, decrease, or remain the same?) Scientifically, why is this?

It remains the same

Explanation: during boiling, the temperature is constant. When heat is added to a liquid at the boiling temperature, the heat (energy) added will only converts the liquid into a gas at the same temperature. the energy added to the liquid goes into breaking the bonds between the liquid molecules without causing the temperature to change. This is true for all substance that vapourizes