(a) ‘X’ and ‘Y’ are C (carbon) and O (oxygen). These combine in ratio of 12:32 i.e., 3:8. ‘Z’ is CO2(carbon dioxide)
(b) ‘X’ is carbon (atomic number 6) so its electronic configuration is 2, 4. ‘Y’ is oxygen (atomic number 8) so its electronic configuration is 2, 6.
(c) ‘Z’ is CO2 so it is made up of one carbon atom and two oxygen atoms so it atomicity is 3 (i.e. triatomic molecule).