Answer
H-C=C-H fails to make sense chemically because in order for the carbons' valence shells to be full in this covalent bonding, there must be 4 bonds to Carbon. Both carbons in this compound only have 3 bonds.
Work Step by Step
This molecule may exist as an intermediate in a chemical reaction, but it is too unstable to exist more than momentarily. Either another hydrogen must be bonded to either carbon (forming ethylene) or the C-C bond must be a triple bond (forming acetylene). These triple bonds are significantly less stable, however, and acetylene is a considerably less preferable arrangement.
