(i) The atomic number of calcium Ca =20
The Electronic configuration of Ca is 2, 8, 8, 2
(ii) Since Rb belongs to 1st group therefore Rb has one valence electron.
(iii) Sr (38) belongs to 5th period. Therefore, Sr has 5 shells.
(v) K belongs to 1st group which means that it has one valence electron and therefore it can donate the electron and attain stable gas configuration. Therefore, it is a metal.
(v) The largest atom in size is Rb.
(vi) The Increasing order of the atomic size of the respective atoms is as follows:
Be < Mg < Ca < Rb
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