Consider the following set of H-bonds :

 

 

 

 

 

 

 

 

 

 

 

 

The correct order of H-bond strength is :

$\mathrm{A}-\mathrm{H}···\mathrm{B}$ for H-bond strength: 

Criteria-1 

A should be more electronegative.

Criteria-2 

B should be less electronegative and ${\mathrm{e}}^{-}$ rich.

Thus, the correct order of H-bond strength is :

P > Q > R > S