Polarization power of cation increases when:

• A. Charge on the cation increases.
• B. Size of the cation increases.
• C. Charge on the cation decreases.
• D. Both charge and size of the cation increase.

To understand how the polarization power of a cation changes, we need to consider two main factors: the charge of the cation and its size. Let's break down the options you've provided and see which one correctly identifies when the polarization power increases.

Defining Polarization Power

Polarization power refers to the ability of a cation to distort the electron cloud of an anion. This distortion can affect the properties of ionic compounds, such as their solubility and melting points. The greater the polarization power, the more significant the distortion of the anion's electron cloud.

Factors Influencing Polarization

There are two key factors that influence the polarization power of a cation:

• Charge of the Cation: A higher positive charge on the cation increases its polarization power. This is because a cation with a higher charge exerts a stronger electrostatic force on the electrons of the anion, leading to greater distortion.
• Size of the Cation: A smaller cation has a higher charge density, which means that the charge is concentrated in a smaller volume. This also enhances its ability to polarize an anion. Conversely, larger cations have lower charge density and thus lower polarization power.

Analyzing the Options

Now, let’s evaluate the options you provided:

• A. Charge on the cation increases: This is true. Increasing the charge enhances polarization power.
• B. Size of the cation increases: This is false. Increasing the size generally decreases polarization power due to lower charge density.
• C. Charge on the cation decreases: This is also false. A decrease in charge would reduce polarization power.
• D. Both charge and size of the cation increase: This is misleading. While an increase in charge would increase polarization, an increase in size would counteract that effect.

Conclusion

The correct answer is A. Charge on the cation increases. This option accurately reflects the relationship between charge and polarization power. To summarize, increasing the charge of a cation enhances its ability to polarize an anion, while increasing the size generally has the opposite effect. Understanding these principles is crucial for predicting the behavior of ionic compounds in various chemical contexts.