The number of elements present in the fourth period is

An element with atomic number $20$ will be placed in which period of the periodic table?

How can the period,group,and block of an element be predicted?

The long form of the periodic table has:

The total number of elements in the $10^{th}$ period of the periodic table will be:

Atomic numbers of three elements $E_1$,$E_2$ and $E_3$ of the periodic table are $Z_1$,$50$ and $Z_2$ respectively. From the position of the elements shown in the figure,the value of $(Z_2 - Z_1)$ is: