Which of the following statements is/are incorrect?
(a) Cassiterite is not the ore of tin
(b) Metallurgy is a process of mixing of ore
(c) concentration of chromite (`FeO.Cr_2O_3`) is done by magnetic separation
(d) ZnS with depressant NaCN forms `Na_2[Zn(CN)_4]`

Options

A. (a) & (b)
B. only (a)
C. (b),(c) & (d)
D. (c) & (d)

Answer

To determine which of the statements are incorrect, let's analyze each statement one by one:

### Step 1: Analyze Statement (a)
**Statement (a):** Cassiterite is not the ore of tin.
- **Analysis:** Cassiterite is actually the primary ore of tin, with the chemical formula SnO2. Therefore, this statement is incorrect.

### Step 2: Analyze Statement (b)
**Statement (b):** Metallurgy is a process of mixing of ore.
- **Analysis:** Metallurgy refers to the processes involved in the extraction of metals from their ores and the refining of those metals. It is not merely a process of mixing ores. Thus, this statement is also incorrect.

### Step 3: Analyze Statement (c)
**Statement (c):** Concentration of chromite (FeO.Cr2O3) is done by magnetic separation.
- **Analysis:** Chromite is indeed a magnetic ore, and it can be concentrated using magnetic separation due to its magnetic properties. Therefore, this statement is correct.

### Step 4: Analyze Statement (d)
**Statement (d):** ZnS with depressant NaCN forms Na2[Zn(CN)4].
- **Analysis:** In the froth flotation process, when zinc sulfide (ZnS) is treated with sodium cyanide (NaCN) as a depressant, it forms the soluble complex Na2[Zn(CN)4]. This statement is correct.

### Conclusion
Based on the analysis:
- Statement (a) is incorrect.
- Statement (b) is incorrect.
- Statement (c) is correct.
- Statement (d) is correct.

Thus, the incorrect statements are (a) and (b).

### Final Answer
The incorrect statements are:
- (a) Cassiterite is not the ore of tin.
- (b) Metallurgy is a process of mixing of ore.