A sulphide of a metal `(M)` with formula `MS` is white coloured ppt which is soluble in acidic solution `(PH lt 6)`. Metal cation M is:

Options

A. `Pb^(2+)`
B. `Zn^(2+)`
C. `Hg^(2+)`
D. `Cu^(2+)`

Explanation

To determine the metal cation \( M \) in the sulfide \( MS \) that forms a white precipitate and is soluble in acidic solutions, we can follow these steps:

### Step 1: Understand the Properties of Sulfides
Sulfides (S²⁻) are generally basic in nature and react with water to produce hydrogen sulfide (HS⁻) and hydroxide ions (OH⁻). This means that in a neutral or basic environment, sulfides are less soluble.

**Hint:** Remember that sulfides can react with acids to form soluble species.

### Step 2: Identify the Characteristics of the Precipitate
The question specifies that the precipitate is white in color and soluble in acidic solutions. This narrows down the possibilities for the metal cation \( M \).

**Hint:** Focus on common metal sulfides that are known to be white and soluble in acids.

### Step 3: Consider Common Metal Sulfides
One of the most well-known white metal sulfides is zinc sulfide (ZnS). It is a white precipitate and is known to dissolve in acidic solutions, forming zinc ions (Zn²⁺).

**Hint:** Recall that zinc sulfide is a common example of a white precipitate that fits the criteria given.

### Step 4: Confirm the Solubility in Acidic Solutions
When zinc sulfide is treated with an acid, it reacts to form soluble zinc ions and hydrogen sulfide gas. This confirms that ZnS meets the criteria of being soluble in acidic conditions.

**Hint:** Check the solubility rules for sulfides in acidic environments to validate your findings.

### Step 5: Conclusion
Based on the properties of the sulfide and the characteristics of the precipitate, the metal cation \( M \) is identified as zinc (Zn²⁺).

**Final Answer:** The metal cation \( M \) is \( \text{Zn}^{2+} \).