Which of the following elements mostly form covalent compounds?

First member of $1st$ group i.e. lithium, mostly form covalent compounds due to its small size and comparatively high $I. E.$ (with respect to other members of its group).&

Covalent character depends upon the atomic radii. Smaller the atomic radii, more the covalent character i.e. the covalent character is inversely proportional to atomic radii.