A solution turns red litmus blue. On adding acid, heat is released and a salt is formed. What type of reaction is this?

Correct answer: Neutralisation reaction

The red-litmus-to-blue change shows that the solution is basic. When an acid reacts with a base, the characteristic products are salt and water; heat is often released because the reaction is exothermic. This is therefore a neutralisation reaction, so option A is correct. Decomposition involves one compound breaking down, displacement involves replacement by another element, and precipitation specifically produces an insoluble solid.