Which one of the following elements symbolised as A and B is a metal, 19A9 or 24B12? Why?
The given data regarding element A and B suggests that the atomic number of element A is 9, while that of element B is 12. Thus, the electronic configuration of element A is 2, 7 while that of element B is 2, 8, 2. These electronic configurations indicate that element A will complete its octet by accepting one electron, while element B will complete its octet by losing 2 electrons present in its valence shell. Out of metals and non-metals, the tendency to lose electrons and form positive ions is shown by metals. So, the element B is metal, while element A is non-metal.