To solve the question, we need to identify two metals, X and Y, that can form two oxides where their valencies differ by two units. Let's break down the solution step by step.
### Step-by-Step Solution:
1. **Understanding Valency and Oxides**:
- Valency refers to the combining capacity of an element, often determined by the number of electrons an atom can lose, gain, or share.
- When metals form oxides, they can exhibit different valencies based on the number of oxygen atoms they bond with.
2. **Identifying Possible Metals**:
- We need to find two metals that can form two oxides with a difference in their oxidation states (valencies) of 2.
- The options given are: copper and iron, iron and lead, lead and tin, or tin and copper.
3. **Examining Each Pair**:
- **Copper and Iron**:
- Copper can form CuO (valency +2) and Cu2O (valency +1). The difference is 1, not 2.
- Iron can form FeO (valency +2) and Fe2O3 (valency +3). The difference is 1, not 2.
- **Iron and Lead**:
- Iron forms FeO (+2) and Fe2O3 (+3), difference is 1.
- Lead forms PbO (+2) and PbO2 (+4), difference is 2.
- **Lead and Tin**:
- Lead forms PbO (+2) and PbO2 (+4), difference is 2.
- Tin forms SnO (+2) and SnO2 (+4), difference is 2.
- **Tin and Copper**:
- Tin forms SnO (+2) and SnO2 (+4), difference is 2.
- Copper forms CuO (+2) and Cu2O (+1), difference is 1.
4. **Conclusion**:
- The only pair of metals that can form two oxides with a valency difference of 2 is **Lead (Pb)** and **Tin (Sn)**.
- Therefore, the answer is **Lead and Tin**.
### Final Answer:
X = Lead (Pb), Y = Tin (Sn).
