Which hydrogen halide has the strongest bond?

The strength of a bond in hydrogen halide depends on the following factors:
1.Atomic size
2.Polarity
3.Bond length
4.Bond energy

Decreasing order of bond strength:

HF ＞ HCl ＞HBr ＞ HI

As hydrogen having one electron in valence shell (belongs to group 1) easily form a bond to complete its duplet. On the other hand,halogens (group 7 elements) having florine is the most electronegative element of the periodic table.
Halogens(F, Cl, Br & I) having 7 valence electrons form a covalent bond with hydrogen to complete its octet ( 8 electrons),result in the formation of covalent bond.

Factors affecting the strength of hydrogen halide are discussed below:

How atomic size affects the strength of a hydrogen halide bond?