Question

An element X has mass number 35 and number of neurones 18 write atomic number in electronic configuration of X also write group number period of valency of X

Answer 1

x is chlorine.
atomic number of chlorine is 17.
electronic configuration of chlorine - 2, 8,7 ( if the above question was meant for class 10-cbse )
group number of chlorine- 17
period of chlorine - 3
valency of chlorine- 1 
hope this answer helps.!. :)