Which one among the following contains the most neutrons?

A stable nucleus (light with $\mathrm{A}<10$ ) has ______.

Match the following

Amongst the following chemical species

$\mathrm{I}.$ ${}_{18}\mathrm{Ar}^{39}$

$\mathrm{II}.$ ${}_{19}{}^{40} {\mathrm{K}}^{+}$

$\mathrm{III}.$ ${}_{20}{}^{40}\mathrm{Ca}^{2+}$

$\mathrm{IV}.$ ${}_{20}{}^{40}\mathrm{Ca}^{+}$

The species having identical electronic configuration are

Match the following.