Why is it necessary to add concentrated HCl, then water, rather than a solution of HCl to the eudiometer tube

The reaction between concentrated acid and water can release a lot of heat. If a little water is added to a larger amount of acid, the heat can cause the small amount of water to boil very rapidly which then spatters some acid. ... It is recommended that acid should be added to water and not water to acid.

The answer is 4 i don't know if its right let me see.