A blue solid is changed into a white substance and a colorless gas. Was the blue solid an element or a compound? Explain your reasoning.?

Elements are the simplest chemical substances, and an element as the sole starting material cannot be chemically transformed into new species. Therefore, we know that the blue solid was a compound and NOT an element. The blue substance evolved (i) a gas, and (ii) a new white substance. Given the formation of the two new species, the starting material could not have been an element.

It is not possible to conclude with certainty whether the blue solid was an element or a compound without knowing more specific details about the identity of the blue solid and the products formed. If the blue solid was an element, it would have had to undergo a chemical reaction to form a new substance, suggesting it was a compound. If it was a compound, the change would involve breaking the bonds between its elements to form the white substance and colorless gas.