Which molecule has a longer and more unstable double bond?

The molecule with a longer and more unstable double bond is sulfur (S2). A double bond generally consists of one sigma bond and one pi bond. In elements like oxygen, nitrogen, and sulfur, the strength and stability of these bonds can vary significantly due to the size of the atoms involved and their electronegativity.

Sulfur is larger than both oxygen and nitrogen, leading to longer bond lengths for its double bonds compared to the double bonds found in O2 and N2. The larger atomic size of sulfur results in greater bond length because the nuclei are farther apart. This increased bond length is associated with a decrease in bond strength and stability, rendering the double bond in S2 more unstable compared to the double bonds in O2 and N2.

In contrast, O2 and N2 both contain double bonds as well, but these are shorter and stronger due to the smaller atomic radii and higher electronegativity of the oxygen and nitrogen atoms. The O=O bond in oxygen is stronger than the S=S bond in sulfur, as the shorter bond length leads to a stronger interaction between the nuclei and the shared electron cloud, thereby resulting in more stability.

H2, on the other hand, contains a single bond with no double bond