The elements Li, Na and K, each having one valence electron, are in period 2, 3 and 4 respectively of modern periodic table.
(a) In which group of the periodic table should they be ?
(b) Which one of them is least reactive ?
(c) Which one of them has the largest atomic radius ? Give reason to justify your answer in each case.

Explanation

(a) Since the elements have one valence electron, they are placed in group 1 (Alkali metals) in the order Li (period = 2) , Na (period = 3) , K (period = 4).
(b) Since the reactivity of the elements increases down a group, the element Li is the least reactive chemically.
(c) Since the atomic size increases down a group, the element K has the large atomic size or atomic radius out of these elements.