Positive ions are formed from the neutral atom by the

Give the relation between the following pairs of species:
$(i)$ $_{20}^{40}Ca$ and $_{19}^{40}K$
$(ii)$ $_{17}^{35}Cl$ and $_{17}^{37}Cl$
$(iii)$ $_{18}^{40}Ar$,$_{20}^{40}Ca$ and $_{19}^{40}K$
$(iv)$ $_{38}^{87}Sr$ and $_{38}^{90}Sr$

What are the similarities and differences between $Mg$ and $Mg^{2+}$?

Which of the following is always a whole number?

When a sulphur atom becomes a sulphide ion,

An isotone of $_{32}^{76}Ge$ is (one or more are correct)