Three elements 'X', 'Y' and 'Z' have atomic numbers 7, 8 and 9 respectively.
(i) State their positions (Group number and period number both) in the Modern Periodic Table.
(ii) Arrange these elements in the decreasing order of their atomic radii.
(iii) Write the formula of the compound formed when 'X' combines with 'Z'.

Explanation

(i) X (7) = 2,5 Group 15, Period 2
Y(8) = 2,6 Group 16, Period 2
Z(9) = 2,7 Group 17, Period 2
(ii) `XgtYgtZ`
(iii) `XZ_(3)`