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.

Explanation

Mass number of element X = 35
Number of neutrons = 18
`:.` Proton or charge number in the atomic number of `X = 35 - 18 = 17.`
The element having atomic number is chlorine
Its electronic configuration is `{:(K, L, M),(2, 8, 7):}`
  Its valency is 8-7 = 1
  X-chlorine belongs to 3rd period and 17 group of modern periodic table.