If an orbital can have maximum 4 electrons then, how may elements can be present in 8th period?

The formula to determine how many elements there are in a particular period is, where n is the number of the period.

If n=8 ,n is even

The number of elements there are in a particular period is,

$$\begin{gathered} = \frac{(n+2)2}{2} \\ =\frac{(8+2)2}{2} \\ =10 \end{gathered}$$

Hence there are 10 elements can be present in 8th period.