The decreasing order of stability of following cations is
(a) P>Q>R>S
(b) S>Q>R>P
(c) P>R>Q>S
(d) R>P >Q >S

In case of P structure ...positive charge is very stable because of resonance and hyperconjugation due to Hs on the methyl on the ortho position. Hs show more effective stabilization due to overlapping of Hs of ortho carbon with empty p orbitals of benzylic carbon .
In Q structure stabilization is not very strong as positive charge is not on meta position and hence less stabilization as compare to ortho and para position .
In para position, stabilization is strong due to resonance and hyperconjugation from methyl Hs.

Its a great explanation so (C) is correct answer thanks mam.