What do you observe (on the basis of energy)when:

(a) an acid is added to a basic solution?

(b) ammonium chloride is dissolved in water?

(a) When an acid is added to a basic solution, a neutralisation reaction takes place. Energy is released during the reaction. So, the temperature of the solution rises and the container may feel warm. This is because neutralisation is an exothermic reaction (gives out heat energy).

(b) When ammonium chloride is dissolved in water, heat is absorbed leading to fall in temperature. So the apparatus in which this reaction occurs becomes colder than earlier.