Question

Assertion: F is more electronegative than Cl.
Reason: F has higher electron affinity than Cl.
(a) If both assertion and reason are true and the reason is a correct explanation of the assertion.
(b) If both assertion and reason are true but reason is not a correct explanation of the assertion.
(c) If the assertion is true but reason is false.
(d) If both the assertion and reason are false.
(e) If the assertion is false but the reason is true.

Answer 1

Hint: Solve this question by applying periodic properties of these elements. There are many factors such as atomic radius, oxidizing/reducing nature (non-metals are oxidizing in nature, i.e., they reduce themselves), acidity, basicity, etc.

Complete step by step answer:
Let us understand the terms ‘electronegativity’ and ‘electron affinity’.
Electronegativity is defined as, “the tendency of an atom in its molecule to attract the shared electron pair towards itself.” It increases with increasing number of electrons in the valence shell, but decreases with increasing atomic size.
Electron affinity is defined as, “the amount of energy liberated when an electron is added to a neutral, isolated atom in its ground state”. It is inversely proportional to atomic size; therefore, it decreases with increase in atomic size.
The assertion states that Fluorine is more electronegative than Chlorine.
Since electronegativity is inversely proportional to atomic size, the given statement is true.
The reason states that Fluorine has higher electron affinity than Chlorine.
Since fluorine has a very small atomic radius, it exerts a repulsive force on any incoming electron. Therefore, Chlorine has a higher electron affinity than Fluorine. So, the given reason is false.
Therefore, the answer is – option (c) – The given assertion is true but the reason is false.

Additional Information:
In a period, halogens have the maximum electron affinity and electronegativity.

Note: In case of electron affinity, students often confuse in the order of decreasing/increasing order. The order is: Cl > F > Br > I.
All periodic properties show some exceptions. Fluorine shows such exceptions due to its very small atomic size. In the periodic table –
- Chlorine has the maximum electron affinity.
- Fluorine has the maximum electronegativity.