Question

Given below are two statements : one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A) : Metallic character decreases and non-metallic character increases on moving from left to right in a period.
Reason (R) : It is due to increase in ionisation enthalpy and decrease in electron gain enthalpy, when one moves from left to right in a period.
In the light of the above statements, choose the most appropriate answer from the options given below :

• A. Both (A) and (R) are correct and (R) is the correct explanation of (A).
• B. Both (A) and (R) are correct but (R) is not the correct explanation of (A).
• C. (A) is true but (R) is false.
• D. (A) is false but (R) is true.

Hint:

Metallic character is directly proportional to atomic radius and inversely proportional to ionization energy. Non-metallic character follows the exact opposite trend.

Answer 1

The Correct Option is A

To correctly address the question, we need to analyze both the Assertion (A) and Reason (R) given, and determine their correctness and the relationship between them.

1. Assertion (A): Metallic character decreases and non-metallic character increases on moving from left to right in a period.

This assertion is based on the periodic trends observed in the periodic table. As we move from left to right across a period, elements gradually change from being metals to non-metals. This is due to the increase in nuclear charge and a corresponding decrease in the size of the atoms, leading to stronger attraction for outer electrons, which is characteristic of non-metals. Therefore, the assertion is true.

2. Reason (R): It is due to an increase in ionization enthalpy and a decrease in electron gain enthalpy when one moves from left to right in a period.

We need to understand the relationship between ionization enthalpy, electron gain enthalpy, and the metallic/non-metallic nature of elements:

• Ionization Enthalpy: It refers to the energy required to remove an electron from an atom. As we move across a period, ionization enthalpy increases due to the increasing effective nuclear charge. This increase in ionization enthalpy is why metals, which lose electrons easily, become less common and non-metals, which do not lose their electrons easily, become more common.
• Electron Gain Enthalpy: It refers to the energy change when an electron is added to a neutral atom. Across a period, while the electron gain enthalpy generally becomes more negative (indicating easier electron gain), it plays a lesser role in defining metallic and non-metallic character compared to ionization enthalpy.

Based on the definitions, the increase in ionization enthalpy as we move across a period does explain why metallic character decreases and non-metallic character increases. Therefore, the reason provided supports and explains the assertion correctly.

Conclusion: Both Assertion (A) and Reason (R) are correct and (R) is the correct explanation of (A). Therefore, the correct option is:

Both (A) and (R) are correct and (R) is the correct explanation of (A).