Which of the following statements, about the advantage of roasting of sulphide ore before reduction is not true?

Options

A. the magnitude of `DeltaG_(f)^(@)` of the sulphide is greater than those for `CS_(2)` and `H_(2)S`
B. the `DeltaG_(f)^(@)` is negative for roasting of sulphide ore to oxide
C. roasting of the sulphide to the oxide is thermodynamically feasible
D. carbon and hydrogen are suitable reducing agents for metal sulphides

Answer

To determine which statement about the advantages of roasting sulfide ore before reduction is not true, we will analyze each statement step by step.

### Step-by-Step Solution:

1. **Understanding Roasting**:
Roasting is a process where sulfide ores are heated in the presence of oxygen. This process converts the sulfide ores into oxides, releasing sulfur dioxide gas. It is often used to prepare ores for further reduction.

2. **Analyzing Statement 1**:
The first statement claims that the standard free energy of formation (ΔG°f) for most sulfides is greater than that of CH2 and H2S. This is true because sulfides are generally more stable than these compounds, which means they have a higher free energy of formation. Thus, this statement is correct.

3. **Analyzing Statement 2**:
The second statement asserts that ΔG°f is negative for the roasting of sulfide ore to oxide. This is also true. The roasting process is thermodynamically favorable, as the formation of metal oxides from metal sulfides typically has a negative ΔG°, indicating that the reaction can proceed spontaneously.

4. **Analyzing Statement 3**:
The third statement discusses the thermodynamic favorability of the roasting process. Since roasting converts sulfides to oxides, and the ΔG°f for the oxides is lower than that of the sulfides, this statement is also correct. The reaction is indeed thermodynamically favorable.

5. **Analyzing Statement 4**:
The fourth statement suggests that carbon and hydrogen can be used as reducing agents for metal sulfides. This statement is not true. Carbon and hydrogen are not effective reducing agents for metal sulfides due to their higher ΔG°f compared to the sulfides, which means they cannot reduce sulfides to metals effectively.

### Conclusion:
The statement that is not true regarding the advantages of roasting sulfide ore before reduction is **Statement 4**.