This question tests understanding of fundamental concepts in redox reactions: oxidation, reduction, oxidising agents, and reducing agents. We need to recall the definitions of these terms to identify the correct answer.
D) Reducing agent (reductant) — This is correct because a reducing agent is defined as a substance that loses electrons (gets oxidised) and, in doing so, causes another substance to gain electrons (get reduced).
The question asks to identify a strong oxidizing agent commonly used in redox titrations, characterized by its intense purple color and self-indicating endpoint. We need to evaluate each option based on these properties.
Correct Option: D) Potassium permanganate (\(\text{KMnO}_4\)) is a strong oxidizing agent. Its intense purple color (due to the \(\text{MnO}_4^-\) ion) and its reduction to a colorless \(\text{Mn}^{2+}\) ion during titration allow it to act as a self-indicator. The appearance of a persistent light pink/purple color from the first excess drop of \(\text{KMnO}_4\) signals the endpoint of the titration.
The question asks about the common use of potassium dichromate (K₂Cr₂O₇) in volumetric analysis. To answer this, we need to understand its chemical properties, specifically its ability to gain or lose electrons in reactions.
B) Oxidising agent - Potassium dichromate is a strong oxidizing agent because chromium is in its highest oxidation state (+6) and readily accepts electrons to get reduced to a lower, more stable oxidation state (+3), thereby oxidizing other substances.
The question asks about the role of sulphur dioxide (SO\(_2\)) in a reaction with hydrogen sulphide (H\(_2\)S), considering its usual behavior as a reducing agent. We need to determine if SO\(_2\) acts as an oxidising agent, reducing agent, or something else in this specific context.
Correct Option: D) Oxidising agent
The question asks to identify a gas that acts as a strong reducing agent, specifically used to reduce heated metal oxides to their corresponding metals. We need to recall the properties of common gases and their roles in redox reactions.
B) Hydrogen is a strong reducing agent commonly used to reduce heated metal oxides to their corresponding metals. It gets oxidized to water in the process.
To determine why ferrous ions (\( \text{Fe}^{2+} \)) act as a reducing agent, we need to understand the definition of a reducing agent and the common oxidation states of iron. A reducing agent is a species that loses electrons (gets oxidized) and causes another species to be reduced. Iron commonly exists in +2 and +3 oxidation states.
Correct Option: D) Fe3+ (ferric ion) by losing an electron
This option correctly identifies that \( \text{Fe}^{2+} \) loses one electron to become \( \text{Fe}^{3+} \), which is an oxidation process, making \( \text{Fe}^{2+} \) a reducing agent.