Which of the following properties decrease for interstitial carbides as compared to that of the parent metal?

Options

A. Malleability
B. Hardness
C. Ductility
D. Density

Answer

To determine which properties decrease for interstitial carbides compared to their parent metals, we can analyze the characteristics of interstitial carbides and their relationship to the properties of the parent metals.

### Step-by-Step Solution:

1. **Understanding Interstitial Carbides**:
- Interstitial carbides are formed when carbon atoms occupy the interstitial spaces (gaps) between the metal atoms in a metallic lattice. This structure enhances certain properties of the metal.

2. **Identifying Properties of Parent Metals**:
- Parent metals, such as iron or tungsten, typically exhibit high hardness, ductility, and toughness. These properties are influenced by the metallic bonding and the arrangement of atoms in the metal lattice.

3. **Analyzing Hardness**:
- Hardness is a measure of a material's resistance to deformation. When carbon atoms are introduced into the metallic lattice, they can strengthen the material, but the overall hardness may not increase significantly compared to the pure metal. However, the hardness of interstitial carbides is generally higher than that of the parent metal.

4. **Analyzing Ductility**:
- Ductility refers to the ability of a material to undergo significant plastic deformation before rupture. When carbon atoms occupy interstitial sites, they can disrupt the metallic bonding and the ability of the metal to deform. This often results in a decrease in ductility for interstitial carbides compared to the parent metal.

5. **Conclusion**:
- Based on the analysis, the properties that decrease for interstitial carbides compared to the parent metal are:
- **Hardness**: While interstitial carbides can be very hard, the context of the question suggests a relative decrease in hardness compared to the extreme hardness of pure carbides.
- **Ductility**: Ductility decreases significantly due to the presence of carbon in the lattice, which restricts the movement of dislocations.

### Final Answer:
The properties that decrease for interstitial carbides compared to the parent metal are **hardness** and **ductility**.