Question

What do elements of the same period in the periodic table have in common?

Answer 1

They all have the same number of occupied electron shells(elements in same period) and same number of atomic orbitals

Answer 2

A period in the periodic table is a row of chemical elements. All elements in a row have the same number of electron shells. Each next element in a period has one more proton and is less metallic than its predecessor.

I hope this helps :)