If four elements with atomic numbers Z-2 , Z-1, Z and Z+1 are forming isoelectronic ions, the atomic number of the ion having largest size is

Step-by-step solution

' Z ' represents number of protons in a nucleus. Therefore, for an isoelectronic species; size of anion > atom > cation. Means the species with more electrons w.r.t. protons in nucleus is of larger size [i.e. has smaller value of Z ]. Thus, Z-2 has least number of protons, whereas Z+1 has maximum number of protons. Hence, order of size for isoelectronic species will be Z-2>Z>Z+1 Element with atomic number Z-2 is of largest size and option (a) is the correct answer.