Which of the following statements is incorrect?

Options

A. In Hall- Heroult process, the electrolyte used is a molten mixture of alumina, sodium hydroxide and cryolite.
B. Lead is extracted form its chief ore by both carbon reduction and self reduction..
C. Tin is extracted from its chief ore by carbon monoxide reduction.
D. Siderite and cassiterite are carbonate ores.

Answer

To determine which of the statements is incorrect, we will analyze each statement one by one.

### Step 1: Analyze Statement A
**Statement A:** In Hall-Heroult process, the electrolyte used is a molten mixture of alumina, sodium hydroxide, and cryolite.

- The Hall-Heroult process is used for the extraction of aluminum. The main components of the electrolyte in this process are alumina (Al₂O₃) and cryolite (Na₃AlF₆).
- Sodium hydroxide (NaOH) is not used in this process as part of the electrolyte.

**Conclusion:** Statement A is incorrect.

### Step 2: Analyze Statement B
**Statement B:** Lead is extracted from its chief ore by both carbon reduction and self-reduction.

- The chief ore of lead is lead sulfide (PbS).
- Lead can be extracted from PbS through roasting, which converts it to lead oxide (PbO) and sulfur dioxide (SO₂).
- PbO can then be reduced by carbon (carbon reduction) to produce lead (Pb) and carbon monoxide (CO).
- Additionally, PbO can also undergo self-reduction with PbS to yield lead and sulfur dioxide.

**Conclusion:** Statement B is correct.

### Step 3: Analyze Statement C
**Statement C:** Tin is extracted from its chief ore by carbon monoxide reduction.

- The chief ore of tin is cassiterite (SnO₂).
- The reduction of SnO₂ can be achieved using carbon monoxide (CO), which reduces SnO₂ to tin (Sn) and produces carbon dioxide (CO₂).

**Conclusion:** Statement C is correct.

### Step 4: Analyze Statement D
**Statement D:** Hydride and cassiterite are carbonate ores.

- Cassiterite (SnO₂) is an oxide ore, not a carbonate ore.
- The term "hydride" does not refer to a specific ore type in this context.
- The correct carbonate ore for iron is siderite (FeCO₃), but this does not relate to cassiterite.

**Conclusion:** Statement D is incorrect.

### Final Conclusion
The incorrect statements are A and D. However, since the question asks for which statement is incorrect, the first statement (A) is clearly incorrect.

### Summary of Incorrect Statements
- **Incorrect Statement:** A (and D, but A is the first one identified).