What will be the $IUPAC$ symbol and name for the element with atomic number $123$?

The electronic configuration of an element $M$ is given below: $M: 1s^2 2s^2 2p^6 3s^2 3p^6 3d^{10} 4s^2 4p^6 4d^{10} 4f^2 5s^2 5p^6 5d^{10} 5f^0 6s^2$. Choose the correct information regarding the element $M$ for its period number,block and group number respectively.

In the fourth period of the periodic table,how many elements have one or more $4d$ electrons?

What is the electronic configuration of the third element of group-$2$ in the periodic table?

What is the main basis for the arrangement of elements in the modern periodic table? Describe it.

Explain the nomenclature of elements having an atomic number greater than $100$.