Why should curd and sour substances not be kept in brass and copper vessels ?

While diluting an acid, why is it recommended that the acid should be added to water and not water to the acid ?

Which gas is usually liberated when an acid reacts with a metal? Illustrate with an example. How will you test for the presence of this gas ?

Compounds such as alcohols and glucose also contain hydrogen but are not categorised as acids. Describe an Activity to prove it.

Name the substance which on treatment with chlorine yields bleaching powder.