Explain in why on addition of 1 mole of NaCl to 1L of water, the boiling point of water increases, while addition of 1 mole of methyl alcohol to 1 L of water decreases its boiling point .

Explanation

NaCl is a non-volatile solute. Its addition to water decreases the vapour pressure of solution. Hence, boiling point of solution increases. On the other hand, methyl alcohol is more volatile than water. Therefore, its addition to water results in increase of vapour pressure. Hence, boiling point of water decreases.