Question

multiple-choice question
periods are the ______ rows in the periodic table.
vertical
horizontal

Explanation:

In the periodic table, periods are defined as the horizontal rows. Vertical columns are called groups. So the correct option is the one with "horizontal".

Answer:

B. horizontal (assuming the options are labeled, but since the original has checkboxes, the correct choice is the "horizontal" option, so the answer is the option with "horizontal", e.g., if we consider the second option as B, then B. horizontal)