The proton numbers in the atoms of some elements, X,Yand Z, are 1, 9,and 20 respectively. (a) State (1) the general name by which elements belonging to the same group in the periodic table with Y are called.
Atomic number 9 is the element fluorine. Fluorine is in group 17 of the periodic table. Elements in group 17 of the periodic table are called halogens.
