How many lone pairs does this molecule have?

Just 1 i.e., Option B.

Because except for top of the molecule, all other sides are filled with a letter meaning there is one free space.

B

Explanation:

H .  +  H .   >  H:H            {":" represents a covalent bond, that is, a shared pair of electrons}

A Lewis structure is a convention used to represent the covalent bonding in a molecule.   Dots or lines are used to represent

valence electrons (electrons available for bonding).  The Lewis structure for the hydrogen molecule is as follows.

     H:H  or  H-H

A bonding pair is an electron pair shared between two atoms.

A nonbonding pair (lone pair, unshared pair) is a pair of electrons that remains on one atom and is not shared.