In 1986, when Halley’s comet last passed the earth, astronomers detected the presence of S2 in their telescopes

Explanation

Sulfur (S) is indeed an element that can form diatomic molecules under certain conditions, such as in the gas phase or at high temperatures. However, sulfur is not commonly found in its diatomic form (S₂) under standard conditions on Earth. Unlike elements like nitrogen (N₂) or oxygen (O₂), which exist as diatomic molecules in their stable gaseous forms at room temperature and atmospheric pressure, sulfur typically exists as a polyatomic molecule or in other chemical compounds.

The presence of S₂ in the spectrum of Halley's comet indicates that sulfur molecules were detected in the comet's coma (a region of gas and dust surrounding the nucleus). This is not a common state for sulfur on Earth's surface due to the prevailing conditions, but in the unique environment of a comet, with its extreme cold and low pressure, sulfur molecules can exist in the diatomic form.