O-H bond is said to be most polar because the electronegativity is different. Electronegativity can be said as the atom's ability to attract electrons towards itself. Electronegativity of an atom increases when there is a movement on the periodic table from left to right.
When the electronegativity between the atoms are different then it is said to be a polar bond on the other case if the electronegativity between the atoms are same it is said to be non- polar bonds.
