Question

the electrons in the atoms of four elements A,B,C and D are distributed in three shells having 1,3,5 and 7 electrons in the outermost shell respectively.state the period in which these elements can be placed in the modern periodic table .write the electronic configuration of the atoms of A and D and the molecular formula of the compound formed when A and D COMBINE

Answer 1

3rd period
hope it helps you

Answer 2

since all the 4 elements are having 3 shells so the PERIOD in which they come in is 3 Period
A- 2,8,1
D-2,8,7
When A and D combines form NaCl