An atom of an element 'A' has three electrons in its outermost shell and that of 'B' has six electrons in the outrer most shell. The formula of the compound formed between these two elements is

If the valence electrons are 1,2,3,4 then generally valency can be taken as 1,2,3,4 respectively.If the valence electrons are 5,6,7 then vlaency is tkaen as 3,2,1 respectivelyThus .... valency of 'A'(Metal) is 3Thus ... Valency of 'B' (Non-metal) is 2A+3B-2A2B3