Which statement about \(\mathrm{H}_{2} \mathrm{~S}\) is true? (1) It is a covalent compound (2) It is a gas with bad smell (3) It is a weak base in water (4) It is a stronger reducing agent than \(\mathrm{H}_{2} \mathrm{O}\) (a) \(1,2,3\) (b) \(2,3,4\) (c) \(1,3,4\) (d) \(1,2,4\)

Covalent compounds, such as hydrogen sulfide (\( \text{H}_2\text{S} \)), are formed when two or more non-metals share electrons in order to obtain a full valence shell and achieve a stable electronic configuration, similar to that of noble gases. This type of chemical bond shapes the physical and chemical properties of the compound.

Hydrogen sulfide is an excellent example of a covalent compound because it consists of sulfur and hydrogen atoms bonded together through shared electrons. Covalent bonds are responsible for the compound's structure and its ability to exist as a discrete molecule, as opposed to ionic compounds, which form a lattice structure.

Gases like hydrogen sulfide have unique physical properties that distinguish them from solids and liquids. Being in a gaseous state at room temperature, \(\text{H}_2\text{S} \) has molecules that are far apart and move freely, leading to an inherent ability to expand and fill any container.

Physical characteristics of gases such as \(\text{H}_2\text{S} \) include low density and high compressibility. Additionally, the distinct odor of hydrogen sulfide, often compared to rotten eggs, is due to the gas's ability to readily diffuse through air, making it detectable even in low concentrations.

The behavior of substances such as hydrogen sulfide in water can reveal their acid or base properties. Acids are substances that can donate protons (\(\text{H}^+ \) ions) to other substances, while bases accept protons. When \(\text{H}_2\text{S} \) dissolves in water, it acts as an acid by donating \(\text{H}^+ \) ions, forming \(\text{HS}^- \) and \(\text{S}^{2-} \) ions in a two-step dissociation process.

This weak acidic behavior is quantified by its dissociation constant (\(\text{K}_\text{a}\)), which is a measure of the compound's tendency to dissociate and donate protons in an aqueous solution, providing insights into the solution's pH level and the compound's reactivity.

Reducing agents are substances that donate electrons to others in chemical reactions, leading to a reduction in oxidation state for certain components. Hydrogen sulfide (\( \text{H}_2\text{S} \) serves as a chemical reducing agent because it readily donates electrons to other substances, thus reducing them while itself being oxidized.

Compared to water (\( \text{H}_2\text{O} \) which typically does not donate electrons, \(\text{H}_2\text{S} \) can act as a strong reducing agent. The ability to act as a reducing agent is crucial in a wide array of chemical processes, such as metal ore processing and organic reactions, and it defines the reactivity and potential applications of hydrogen sulfide in various industrial settings.