Primary nitro compounds when react with `HNO_2` forms crystalline solids which on treatment with `NaoH` gives

Secondary nitro compounds when react with HNO_2 forms crystalline solids which one on treatment with NaOH gives

Ethyl amine reacts with HNO_2 to form

Methyl amine when reacts with HNO_2 produces

An element A reacts with water to form a compound B which is used in white washing. The compound B on heating forms an oxide C which on treatment with water gives back B. Identify A, B and C and give the reactions involved.