P 6 = 2, 4

  Q 11 = 2, 8, 1

  R 15 = 2, 8, 5

  S 17 = 2, 8, 7

  Given the above is the electronic arrangement of PQRS elements, Q will form an electrovalent bond with S. Without argument, D is the answer because electrovalency involves the transfer of electron. Already, Q is 11 with electronic configuration of 2, 8, 1, i.e. having 1 valence electron which is ready to be lost by the atom of element Q, also, S is 17, with electronic configuration of 2, 8, 7. There the 7 valence electron of S attracts that only 1 electron to attain a stable octet structure.