i. X has atomic number 17 i.e. Cl and its electronic configuration is (2,8,7). Thus, its valency is 1. Y has atomic number 20 i.e. Ca and its electronic configuration is (2,8,8,2). Thus, its valency is 2.
∴ The compound will be YX2 i.e. CaCl2
ii. X accepts electron, therefore, it is a nonmetal; Y donates electrons, so it is a metal.
iii. Y has valency 2 and oxygen also has valency 2.
∴ Formula of oxide of Y is YO i.e. CaO.