Consider the following compounds: (P) 1-(4-methoxyphenyl)ethan-1-ol (Q) 1-phenylethan-1-ol (R) 1-(4-nitrophenyl)ethan-1-ol (S) Phenol The decreasing order of their rate of acid-catalyzed dehydration is:

Step-by-step solution

The rate of acid-catalyzed dehydration of alcohols depends on the stability of the intermediate carbocation formed after the protonation and loss of a water molecule. For (P), the intermediate is the 1-(4-methoxyphenyl)ethyl cation, which is highly stabilized by the +M effect of the methoxy group. For (Q), the intermediate is the 1-phenylethyl cation, stabilized by resonance with the benzene ring. For (R), the intermediate is the 1-(4-nitrophenyl)ethyl cation, which is strongly destabilized by the -M and -I effects