K) with EDTA (ethylenediaminetetraacetic acid) is:

The Irving-Williams series ranks the stability of metal complexes based on the number of d electrons. The series states that as the atomic number of the metal ion increases, the stability of the metal complexes increases up to the middle of the transition series, and then decreases.

EDTA is a hexadentate ligand that can form six bonds with a metal ion. The stability of the metal-EDTA complex increases with the number of bonds formed.

The highest overall stability constant (log K) with EDTA is observed for the metal ion that forms the most stable complex with EDTA. According to the Irving-Williams series, this metal ion is likely to have a partially filled d orbital.

The first row transition metals have the following electronic configurations in their ground state:

Sc: [Ar] 3d1 4s2
Ti: [Ar] 3d2 4s2
V: [Ar] 3d3 4s2
Cr: [Ar] 3d5 4s1
Mn: [Ar] 3d5 4s2
Fe: [Ar] 3d6 4s2
Co: [Ar] 3d7 4s2
Ni: [Ar] 3d8 4s2
Cu: [Ar] 3d10 4s1
Zn: [Ar] 3d10 4s2

Out of these, Cu and Zn have completely filled d orbitals and are not expected to form stable complexes with EDTA. Sc, Ti, and V have partially filled d orbitals, but they are not expected to form highly stable complexes with EDTA.

According to the Irving-Williams series, the highest stability is expected for the metal ions with the electronic configurations of d4 to d7, which includes Cr, Mn, Fe, and Co.

Out of these, Fe has the highest overall stability constant with EDTA. The electronic configuration of Fe2+ is [Ar] 3d6, which is in the range of d4 to d7. Fe can form six bonds with EDTA, resulting in the formation of a highly stable complex.

Therefore, the number of d electrons for the first row transition metal ion having the highest overall stability constant (log K) with EDTA is 6, which corresponds to Fe2+.