Question

Assertion: Reactivity of alkali metals decreases down the group-1.

Reason: Atomic size of the alkali metal atoms increases down the group-1.

Mark the correct choice as:

• A. Both assertion and reason are true and the reason is the correct explanation of assertion.
• B. Both assertion and reason are true but the reason is not the correct explanation of assertion.
• C. Assertion is true but the reason is false.
• D. Assertion is incorrect but reason is correct.

Answer 1

The correct option is D

Assertion is incorrect but reason is correct.

Explanation for assertion statement:

1. As we go down the group, the number of shells increases due to the increases in atomic size and the outermost electron gets further away from the nucleus.
2. It becomes easy to eject this valence electron and hence reactivity increases down the group-1.
3. Hence assertion is incorrect.

Explanation for reason statement:

1. As we go down the group, the number of shells increases so the distance from the centre of the nucleus to the outermost shell increases i.e., the atomic size increases. Due to this the Ionization potential decreases (amount of energy required to eject an electron from the outermost shell of a gaseous isolated atom), and hence tendency to release electron increases. This means metallic character increases, so reactivity also increases.

Hence, D) Assertion is incorrect but reason is correct.