Assertion: Alkali metals have low densities.
Reason: Alkali metals have relatively large atomic radii due to the shielding effect of their inner electrons, resulting in low densities.
Both Assertion (A) and Reason (R) are the true and Reason (R) is a correct explanation of Assertion (A).
Both Assertion (A) and Reason (R) are the true but Reason (R) is not a correct explanation of Assertion (A).
Assertion (A) is true and Reason (R) is false.
Assertion (A) is false and Reason (R) is true.
The assertion is true because alkali metals have relatively large atomic radii compared to other metals. This is due to the shielding effect of their inner electrons, which reduces the attraction between the outermost electrons and the positively charged nucleus. This results in low densities, as the mass of the atoms is spread out over a larger volume.