An unknown substance "A" on thermal decomposition produces "B" and "C".What is A, an element or compound. Give reason

Dear Student,

A is a compound because compound can undergo thermal decomposition to gives other compound while element on providing heat to them do not give anything. So A should be compound.

For example : Iron sulphate on heating gives ferric oxide, sulphur dioxide and sulphur trioxide.

    FeSO4 $\stackrel{heat}{\to }$ Fe₂O₃ +SO₂+SO3

Regards