What is common about the elements of a period? select all that apply. they have the same number of electron energy levels. they have similar chemical characteristics. they have similar physical characteristics. they transition from a metal to noble gas.

They have the same number of electron energy levels.

They transition from a metal to noble gas.

Explanation:

Periods in the periodic table of elements refer to elements in the same row. All the elements in a certain row of the periodic table;

have the same number of electron energy levels.

transition from a metal to noble gas.

it means there are 3 atoms of oxygen