Sometimes, it is possible to separate two sulphide ores by adjusting proportion of oil to water or by using depressants. In case of an ore containing ZnS and PbS, the depresent used is

Options

A. NaCN prevents PbS from coming to the froth but allows ZnS to come with froth .
B. NaCN prevents ZnS from coming to the froth but allows PbS to come with froth.
C. NaCN prevents frothing of both ZnS and PbS, hence no froth is formed.
D. NaCN does not act as depressant hence a mixture of PbS and ZnS is found in froth.

Answer

To solve the question regarding the separation of zinc sulfide (ZnS) and lead sulfide (PbS) using a depressant, we can follow these steps:

### Step 1: Understand the Concept of Depressants
A depressant is a substance used in the froth flotation process to selectively inhibit the flotation of one mineral while allowing the other to float. In this case, we are dealing with two sulfide ores: ZnS and PbS.

**Hint:** Remember that a depressant selectively affects one type of mineral, allowing the other to be collected in the froth.

### Step 2: Identify the Depressant Used
In the case of separating ZnS from PbS, sodium cyanide (NaCN) is commonly used as a depressant. NaCN selectively reacts with ZnS, making it soluble in the solution, while PbS remains unaffected and can be collected in the froth.

**Hint:** Look for the chemical behavior of the depressant with respect to the minerals involved.

### Step 3: Analyze the Options
Now, let’s analyze the options provided in the question:
1. NaCN prevents lead sulfide from coming to the froth but allows ZnS to come with froth.
2. NaCN prevents ZnS from coming to the froth but allows lead sulfide to come with froth.
3. NaCN prevents floating of both ZnS and lead sulfide; hence no froth is formed.
4. NaCN does not act as a depressant; hence a mixture of lead sulfide and zinc sulfide is found in the soil.

From our understanding, the correct statement is that NaCN prevents ZnS from coming to the froth while allowing PbS to float.

**Hint:** Focus on the effect of the depressant on each mineral to determine the correct option.

### Step 4: Conclusion
Based on the analysis, the correct answer is:
**NaCN prevents ZnS from coming to the froth but allows lead sulfide (PbS) to come with the froth.**

**Final Answer:** The depressant used is NaCN, which prevents ZnS from floating while allowing PbS to float.