The decreasing order of stability of following cations is
(A)P>Q>R>S                                                                                       
(B)Q>S>R>P
(C)Q>P>S>R   
(d) Q >P >R >S

These all are primary benzylic carbocations with different EDGs on the ring,
-NH2 is the best EDG as N is less EN and has a lone pair which can stabilize it.
-OH is next as it also has lone pair on it.
Methyl can stabilize through hyperconjugation
and Cl is the weakest electron donating group.So order is
Q>P>R>S

Its a great explanation so (D) is correct answer thank you.