. An element X belongs to 3rd period and group 17 of the periodic table
State its (i) electronic configuration, (ii) valency. Justify your answer with reasoning
Ans. (i) Electronic configuration. 'X' has three energy shells-K, L, M (as it belongs to the 3rd
period and the period number of an element is equal to the number of shells in its atom).
'X' has 7 valence electrons since the group number of an element having more than 2 valence electrons is equal to the valence electrons plus 10.