In which of the following compounds sulphur exhibit lowest oxidation state?

Hydrogen sulphide

The correct answer is option 3. Hydrogen sulphide.

Let us delve into the oxidation states of sulphur in each compound mentioned to understand why hydrogen sulphide (\(H_2S\)) exhibits the lowest oxidation state among the options provided.

1. Sulphur Dioxide (\(SO_2\)):

In \(SO_2\), sulphur is bonded to two oxygen atoms. Oxygen typically exhibits an oxidation state of -2 in compounds (except in peroxides and superoxides). Therefore, to balance the charges:

\(2 \times (-2) + x = 0\)

\(x = +4\)

Thus, sulphur in \(SO_2\) has an oxidation state of +4.

2. Sulphur Monochloride (\(SCl_2\)):

In \(SCl_2\), sulfur is bonded to two chlorine atoms. Chlorine typically has an oxidation state of -1 in compounds (except in compounds with more electronegative atoms). Therefore, to balance the charges:

\(2 \times (-1) + x = 0\)

\(x = +2\)

Thus, sulphur in \(SCl_2\) has an oxidation state of +2.

3. Hydrogen Sulphide (\(H_2S\)):

In \(H_2S\), sulphur is bonded to two hydrogen atoms. Hydrogen typically exhibits an oxidation state of +1 in compounds. Therefore, to balance the charges:

\(2 \times (+1) + x = 0\)

\(x = -2\)

Thus, sulphur in \(H_2S\) has an oxidation state of -2.

4. Oleum (\(H_2SO_4\)):

Oleum is a solution of sulphur trioxide (\(SO_3\)) in concentrated sulphuric acid (\(H_2SO_4\)). In \(H_2SO_4\), sulphur typically has an oxidation state of +6 because sulphuric acid can be viewed as derived from sulphur trioxide:

\(\text{Sulphur in } SO_3: +6\)

\(\text{Sulphur in } H_2SO_4: +6\)

Among the compounds listed, hydrogen sulphide (\(H_2S\)) has the lowest oxidation state for sulfur, which is -2. This is because hydrogen sulphide (\(H_2S\)) contains sulphur in the form of \(S^{2-}\) ions, where sulphur exhibits its lowest oxidation state of -2 due to bonding with hydrogen atoms.

Therefore, the correct answer remains: (3) Hydrogen sulphide (\(H_2S\)).

This compound has sulphur in its lowest oxidation state among the options provided, illustrating the versatility of sulphur in different oxidation states depending on its chemical environment.