[Ahmed Abdullah]

With which of the following elements, Cl forms the strongest covalent bond?
A. Hydrogen B. Carbon C. Phosporus

Does this question have anything to do with atomic orbital theory ( orbitals of similiar energy etc)?

[nj_bartel]

I'd say it has most to do with electronegativity and atomic radius.

[Hello12]

i would say phosphurus, its to do with elements of different electronegativity, which leads to Dipole-dipole forces

[Tyler Durden]

Refer to the periodic trend of electronegativity. Remember that the elements get more electronegative as you move to the right of the periodic table and gets less electronegative as you move down the periodic table. Thus, the farther apart two elements are in the periodic table, the more polar the bond is going to be.