O, F, N in order of increasing strength of hydrogen bonding (X − H − X) is

The strength of the hydrogen bonding depends on the electro negativity of the atom of element. If the electronegativity difference between X and H is maximum then the hydrogen bond is strong.

Here, X is N,O, F etc…

The increasing order of electro negativity of O, F, and N is given below.

$\mathrm{N}<\mathrm{O}<\mathrm{F}$