Answer is: H₂ (molecule of hydrogen).
Missing question: A) LiH B) H₂O C) H₂S D) H₂.
1) In lithium hydride (LiH), lithium has oxidation number +1, than hydrogen must have oxidation number -1, because compound has neutral charge.
2) In water molecule (H₂O), oxygen has oxidation number -2 and hydrogen has +1: 2x + (-2) = 0; x = +1.
3) In hydrogen sulfide (H₂S), sulfur has oxidation number -2 and hydrogen has +1: 2x + (-2) = 0; x = +1.
4) In molecule of hydrogen there is nonpolar covalent bond.