Correct Answer - C
Since the alkali metal salt gives a yellow colour in the flame , it must be sodium salt . Further , since the salt gives an insoluble white ppt. with `BaCl_(2)` in acidic medium , it must be sodium sulphate , `Na_(2)SO_(4)`.
`Na_(2)SO_(4) + BaCl_(2) to underset("White ppt.")(BaSO_(4)) darr + 2 NaCl`