The incorrect statement among the following is

Options

A. Hydrogen is used to reduce NiO
B. Zirconium is refined by van Arkel method
C. The sulphide ore galena is concentrated by froth floatation
D. In the metallurgy of iron, the flux used is `SiO_2`

Explanation

To determine the incorrect statement among the provided options, we will analyze each statement one by one:

1. **Statement 1**: "Hydrogen is used to reduce nickel oxide."
- This statement is **correct**. Hydrogen can indeed be used as a reducing agent to convert nickel oxide (NiO) into nickel (Ni).

2. **Statement 2**: "Zirconium is refined by van Arkel method."
- This statement is also **correct**. The van Arkel method is a process used to purify zirconium by converting it into zirconium tetraiodide, which is then decomposed to yield pure zirconium.

3. **Statement 3**: "Sulphide and galena is concentrated by froth flotation."
- This statement is **correct** as well. Froth flotation is a common method used to concentrate sulfide ores, including galena (PbS), by separating them from the gangue.

4. **Statement 4**: "In the metallurgy of iron, the flux used is SiO2."
- This statement is **incorrect**. In the metallurgy of iron, the flux used is calcium oxide (CaO), not silicon dioxide (SiO2). SiO2 is an acidic impurity, and calcium oxide is used to remove it by forming a slag.

Based on the analysis, the incorrect statement is:

**Final Answer**: The incorrect statement is: "In the metallurgy of iron, the flux used is SiO2."

---