Which of the following metal shows variable valency ?

Options

A. Lead
B. Potassium
C. Calcium
D. Aluminium

Answer

To determine which metal shows variable valency, we need to analyze the valency of the given metals. Let's break down the solution step by step:

### Step 1: Understand Variable Valency
Variable valency refers to the ability of a metal to exhibit more than one oxidation state or valency. This is common in transition metals and some post-transition metals.

**Hint:** Look for metals that can form ions with different charges.

### Step 2: Identify the Metals
In this case, we are considering lead (Pb), potassium (K), calcium (Ca), and aluminum (Al).

**Hint:** List the metals and their common oxidation states.

### Step 3: Analyze Lead (Pb)
Lead is known to exhibit two oxidation states: +2 and +4. This is due to its position in the carbon family (Group 14) of the periodic table. The +4 state is typical for carbon family elements, but lead also shows a stable +2 state due to the inner pair effect.

**Hint:** Check if the metal belongs to a group that typically shows variable valency.

### Step 4: Analyze Potassium (K)
Potassium typically shows a single oxidation state of +1 (K+). It does not exhibit variable valency.

**Hint:** Metals that are in Group 1 usually have a fixed valency.

### Step 5: Analyze Calcium (Ca)
Calcium is an alkaline earth metal and primarily shows a +2 oxidation state (Ca2+). It does not exhibit variable valency.

**Hint:** Alkaline earth metals usually have a fixed valency.

### Step 6: Analyze Aluminum (Al)
Aluminum typically shows a +3 oxidation state (Al3+). It does not exhibit variable valency.

**Hint:** Consider the group of metals and their common oxidation states.

### Conclusion
Among the metals listed, lead (Pb) is the only one that shows variable valency, as it can exist in both +2 and +4 oxidation states. Therefore, the correct answer is lead.

**Final Answer:** Lead (Pb) shows variable valency.