To find the molecular formula from the empirical formula, you need to find a multiple (x) that will give you the molar mass of the compound which in the question is 54 g/mol.
If C₂H₃ is the empirical formula molar mass of empirical formula = (12 × 2) + (1 × 3) g/mol = 27 g/mol let x = multiple let molecular formula = C₂ₓ H₃ₓ
multiple = molecular mass ÷ empirical mass = 54 g/mol ÷ 27 g/mol = 2
