To check the principle of multiple proportions, a series of pure binary compounds P m Q n were analysed and their composition is tabulated below. The correct option(s) is(are) Compound Weight % of P Weight % of Q 1 50 50 2 44 . 4 55 . 6 3 40 60
C. If empirical formula of compound 2 is PQ , then the empirical formula of the compound 1 is P 5 Q 4 .
(A) If empirical formula of 3 is P 3 Q 4 , then molecular formula is P 3 Q 4 n ⇒    3 M P 3 M P + 4 M Q = 40 100 = 2 5 15 M p = 6 M p + 8 M Q 9 M P = 8 M Q ∴ For P 3 Q 5 , % of P = 3 M P 3 M P + 5 M Q × 100 = 8 M Q 23 M Q × 100 = 34 . 78 % (B) If empirical formula of compound 3 is P 3 Q 2 , we have 3 M P 3 M P + 2 M Q = 2 5 15 M P = 6 M P + 4 M Q 9 Mp = 4 M Q If M p = 20 M Q = 180 4 = 45 (C) If empirical formula of 2 is PQ ∴    M P M P + M Q = 4 9 = 44 . 44 100 9 Mp = 5 Mp + 4 MQ 5 M P = 4 M Q If empirical formula is assumed as P 5 Q 4 , % of P = 5 M P 5 M P + 4 M Q × 100 = 50 Hence P 5 Q 4 is the empirical formula of compound (D) If empirical formula of I is P 2 Q , we have %   of   P = 2 M P 2 M P + M Q × 100 = 50 4 M p = 2 M p + M Q 2 M p = M Q Hence, atomic weight of P and Q cannot be 70 and 35 respectively.
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