Classify the elements having atomic numbers `(9,12,16,34,53,56)` into three separate pairs on the basis of similar chemical properties.

Explanation

The second period ends at atomic number 10 while the third period ends at atomic number 18. Therefore 9, 12 and 16 are the first elements in their respective groups. The atomic number of the other elements of the same groups can be deduced by adding magic numbers of 8 ,18 ,18 and 32 to the atomic numbers of the elements of 2nd period or by adding magic number of 18, 18 and 32 to the elements of 3rd period. Thus
`9 + 8 + 18 + 18 = 53`
` 12 + 8 + 18 + 18 = 56`
` 16 + 18 =34`
elements with atomic numbers 9 ( F ) and 53 ( I ) belong to halogen family (Group 17) , elements with atomic numbers 12 (Mg ) and 56 (Ba ) belong to alkaline earth metals (Group 2 ) while elements with atomic numbers 16(S) and 34 (Se ) belong to oxygen family (Group 16 ) For electronic configuration arefer to the text.