Question

Why curd and sour substances should not be kept in metal containers

Answer 1

they are not kept in metal containers. Curd and sour substances contain acid.They would react with the surface of metal vessels such as that of brass and copper to produce harmful substances. curd and sour
things have acid in them. so they are sour.

Hope this will be helpful

Answer 2

Because acid which present in sour and curd would react with metal and will form poison