Let P = hexa-1,3,5-triene, Q = ethenylbenzene (styrene), R = naphthalene and S = biphenyl (two benzene rings joined by a single bond). Which option arranges them in increasing order of degree of unsaturation?

A $P < R < Q < S$
B $P < Q < R < S$
C $Q < P < R < S$
D $P < Q < S < R$

Answer: B

Find the molecular formula and use DU = (2C + 2 - H)/2. P is C6H8 with DU 3. Q is C8H8 with DU 5 (4 for the ring plus 1 for the vinyl C=C). R is C10H8 with DU 7. S is C12H10 with DU 8. The order is P (3) < Q (5) < R (7) < S (8).

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Let P = hexa-1,3,5-triene, Q = ethenylbenzene (styrene), R = naphthalene and S = biphenyl (two benzene rings joined by a single bond). Which option arranges them in increasing order of degree of unsaturation?

Answer: B

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