The elements `""_4Be, ""_12Mg` and `""_20Ca` , each having two valence electrons in their valence shells, are in periods 2, 3 and 4 respectively of the Modern Periodic Table. Answer the following questions associated with these elements, giving reason in each case:
(a) In which group should they be? (b ) Which one of them is least reactive? (c) Which one of them has the largest atomic size?

Explanation

(a) In group 2, as each element has two valence electrons.
(b) Be is least reactive because Be has the least tendency to lose electrons.
(c) Ca has the largest atomic size as Ca has the maximum number of shells and atomic size increases down the group.