A person shows strong unusual hypersensitive reactions when ecposed to certain substances present in the air, identify the condition.. Name the cells responsible for such reactions. What precaution should be taken to avoid such reactions.

What happens when an aqueous solution of sodium sulphate reacts with an aqueous solution of barium chloride? State the physical conditions of reactants in which the reaction between them will not take place. Write the balanced chemical equation for the reaction and name the type of reaction.