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

Options

A. Z-2
B. Z-1
C. Z
D. Z+1

Answer

A

Explanation

` because .Z.` represents number of protons in a nucleus .
Therefore , for an isoelectronic species ,
size of anion ` gt ` atom ` gt ` cation . Means the species larger size [i.e. has smaller value of Z].
Z+ 1 has maximum number of protons.
Hence , order of size for isoelectronic species will be
` Z - 2 gt Z gt Z + 1 `
Element with atomic number Z- 2 is of largest size and option (a) is the correct answer .