The increasing order of the strength of hydrogen bond in the following mentioned linkages is :

(P) $\mathrm{O}-\mathrm{H}\cdots \mathrm{S}$             (Q)$\mathrm{S}-\mathrm{H}\cdots \mathrm{O}$

(R) $\mathrm{F}-\mathrm{H} \cdots {\mathrm{F}}^{-}$         (S)$\mathrm{F}-\mathrm{H}\dots \mathrm{O}$

Most electronegative is F, which is. As a result, R has the strongest hydrogen bonds. S is the least electronegative in Q. Therefore, at Q, the hydrogen bond's strength is at its lowest.