• # question_answer 10) An element 'X' has mass number 35 and number of neutrons 18. Write atomic number and electronic configuration of 'X'. Also write group number, period number and valency of 'X'.

 Atomic no. of X = $3518=17$ Electronic configuration = 2, 8, 7 Group number = 17 Period number = 3 Valency = 1