Maharashtra Board Solutions for Chapter: Periodic Classification of Elements, Exercise 5: Use your brain power

Position of the elements in the periodic elements.

How is the problem regarding the position of cobalt $\left({}_{59}\mathrm{Co}\right)$ and nickel $\left({}_{59}\mathrm{Ni}\right)$ in Mendeleev’s periodic table resolved in the modern periodic table?

Position of the elements in the periodic elements.

How did the position of ${}_{17}{\mathrm{Cl}}^{35}$ and ${}_{17}{\mathrm{Cl}}^{37}$ get fixed in the modern periodic table?

Position of the elements in the periodic elements.

Can there be an element with atomic mass $53$ or $54$ in between the two elements, chromium ${\mathrm{Cr}}_{24}$ and manganese ${\mathrm{Mn}}_{25}$?

Position of the elements in the periodic elements.

What do you think? Should hydrogen be placed in the group $17$ of halogens or group $1$ of alkali metals in the modern periodic table?