ANS:A - base and strong acid.

The heat of neutralization remains constant when there is a reaction between dilute solutions of strong acid and strong base. Explanation: The heat of neutralization is the heat released when an acid and a base react to form a salt and water in a neutralization reaction. In an ideal scenario, where the reaction takes place under constant pressure and the resulting solution is dilute, the heat of neutralization is constant and independent of the specific acid and base used. When a strong acid reacts with a strong base in a dilute solution, such as hydrochloric acid (HCl) and sodium hydroxide (NaOH), the resulting neutralization reaction releases a constant amount of heat per mole of water formed. This is because strong acids and strong bases completely dissociate into ions in solution, resulting in a highly exothermic reaction that generates a consistent amount of heat. However, if one or both of the reactants are weak acids or bases, the heat of neutralization may not be constant. Weak acids and bases only partially dissociate in solution, leading to incomplete neutralization and potentially varying amounts of heat released during the reaction. Therefore, the heat of neutralization remains constant when there is a reaction between dilute solutions of strong acid and strong base.