Heat liberated when 100 ml of 1 N NaOH is neutralized by 300 ml of 1N HCl is
5.73 kJ
NaOH is the limiting reactant (available in smaller proportion).
Heat of formation of water is 57.3 kJ/mol, this is the underlying reaction that happens when acids and bases neutralise too.
Also, normality is the same as normality here.
∴ Heat liberated =57.3 kJ1 mol×1 mol1 L×1 L1000 mL×100 mL=5.73 kJ