If we add impurity to a metal those atoms also deflect electrons . Therefore ,

Options

A. The electrical and thermal conductivities both increase
B. The electrical and thermal conductivities both decrease
C. The electrical conductivity increase but thermal conductivity decrease
D. The electrical conductivity decrease but thermal conductivity increases

Answer

To solve the question regarding the effect of adding impurities to a metal and how it influences the deflection of electrons, we can break down the explanation step by step.

### Step-by-Step Solution:

1. **Understanding Impurities in Metals**: When impurities are added to a pure metal, these foreign atoms disrupt the regular arrangement of the metal's crystal lattice. This disruption affects how electrons move through the material.

**Hint**: Consider how the arrangement of atoms in a metal affects electron flow.

2. **Deflection of Electrons**: The presence of impurity atoms causes scattering of conduction electrons. As electrons move through the metal, they encounter these impurity atoms, which deflect them. This scattering increases the resistance of the metal.

**Hint**: Think about how obstacles in a path can affect movement.

3. **Impact on Resistance**: The increase in resistance due to the scattering of electrons means that it becomes more difficult for electric current to flow through the material. This is a key point because resistance is inversely related to conductivity.

**Hint**: Remember the relationship between resistance and conductivity.

4. **Effect on Conductivity**: Since conductivity is defined as the ability of a material to conduct electric current, an increase in resistance leads to a decrease in electrical conductivity. This means that as we add more impurities, the electrical conductivity of the metal decreases.

**Hint**: Recall the formula for conductivity: \( \sigma = \frac{1}{R} \) where \( \sigma \) is conductivity and \( R \) is resistance.

5. **Thermal Conductivity**: Similarly, thermal conductivity is also affected. The increased resistance and scattering of electrons not only impede electrical flow but also hinder the transfer of thermal energy. Thus, thermal conductivity decreases as well.

**Hint**: Consider how the movement of electrons relates to the transfer of heat.

6. **Conclusion**: Therefore, when impurities are added to a metal, both electrical and thermal conductivity decrease due to the increase in resistance caused by the deflection of electrons by impurity atoms.

**Hint**: Summarize the overall effect of impurities on both types of conductivity.

### Final Answer:
Adding impurities to a metal results in an increase in resistance, which leads to a decrease in both electrical and thermal conductivity.