The correct option for the question is **D. iron (III) chloride**. Let's break down the reasoning step-by-step. ### Explanation of the Correct Answer (D) 1. **Understanding the Reaction**: When hydrogen sulfide (H₂S) gas is passed into a solution of pure iron(II) chloride (FeCl₂), a chemical reaction occurs. Hydrogen sulfide is a reducing agent and can react with iron(II) ions (Fe²⁺) to form iron sulfide (FeS), which is a solid that appears as a yellow deposit. The reaction can be represented as: \[ \text{Fe}^{2+} + \text{H}_2\text{S} \rightarrow \text{FeS} \downarrow + 2\text{H}^+ \] Here, FeS is the yellow precipitate that forms. 2. **What Happens After Filtration**: After filtering out the yellow iron sulfide precipitate, we are left with a solution that contains the remaining ions. Since we started with iron(II) chloride, and some of the iron(II) ions have been removed as FeS, the remaining solution will contain unreacted iron(II) ions and chloride ions. 3. **Oxidation of Iron(II) to Iron(III)**: In the presence of oxygen or air, iron(II) ions can be oxidized to iron(III) ions (Fe³⁺). This oxidation can happen in the solution after the filtration process, especially if the solution is exposed to air. The pale green color of the solution indicates the presence of iron(II) ions, which can appear greenish in dilute solutions. 4. **Final Composition of the Solution**: Therefore, after the yellow precipitate (FeS) is removed, the pale green solution left behind primarily contains iron(II) ions (Fe²⁺) and chloride ions (Cl⁻). If the solution were to be further oxidized, it could eventually turn into iron(III) chloride (FeCl₃), which is yellow-brown in color, but initially, it remains pale green due to the presence of Fe²⁺. ### Why the Other Options Are Incorrect - **A. Dilute Sulphuric Acid**: This option is incorrect because the reaction does not produce sulfuric acid. The presence of H₂S does not lead to the formation of sulfuric acid in this context. Instead, it leads to the formation of iron sulfide and leaves behind iron(II) ions in solution. - **B. Dilute Hydrochloric Acid**: This option is also incorrect. While iron(II) chloride is soluble in hydrochloric acid, the solution left after filtering out the precipitate is not hydrochloric acid. The solution contains iron(II) ions and chloride ions, but it is not simply hydrochloric acid. - **C. Unreacted Hydrogen Sulfide in Water**: This option is incorrect because hydrogen sulfide would not remain in significant amounts in the solution after the reaction. The H₂S gas reacts with the iron(II) ions to form the precipitate, and any unreacted H₂S would be minimal and not the primary component of the solution. ### Summary of Key Points - The yellow deposit formed is iron sulfide (FeS) when H₂S reacts with iron(II) chloride. - The pale green solution left after filtration contains unreacted iron(II) ions and chloride ions. - The oxidation of iron(II) to iron(III) can occur in the presence of air, but the initial solution remains pale green due to Fe²⁺. - The correct answer is **D. iron (III) chloride**, as it reflects the composition of the solution after the reaction and filtration process. This thorough understanding of the chemical reactions and the properties of the compounds involved will help in answering similar questions in the future.