At elevated temperature (~1000 K) the dominant form of sulphur is:

The correct option is S₂.

At room temperature, the most stable allotrope of sulphur is rhombic sulphur, which consists of octasulfur ($S_8$) rings. When sulphur is heated, it undergoes various phase transitions, converting into monoclinic sulphur and eventually melting into a liquid consisting of chains and rings of various sizes.

At elevated temperatures (around 1000 K or above), sulphur exists in the vapor phase. In this vapor state, the larger $S_8$ rings thermalize and break down into smaller, simpler molecular species due to the high thermal energy.
At temperatures near 1000 K, the dominant species in the vapor is the diatomic sulphur molecule, S₂.

Like the diatomic oxygen molecule ($O_2$), the $S_2$ molecule has two unpaired electrons in its antibonding ${\pi }^{*}$ molecular orbitals, making it paramagnetic in nature. Therefore, at ~1000 K, sulphur predominantly exists as paramagnetic S₂ molecules.