Answer:
D. Period
Explanation:
In the periodic table, elements are arranged by rows and columns. Rows are called periods, and columns are called groups. If you look at the periodic table below, you will see that Oxygen, Carbon, and Nitrogen are all in separate columns, so they are not in the same group. However, when you look at them by row, they fall in the same line. This means that they belong in the same period.
They fall in period 2.
