Answer: Option (c) is the correct answer.
Explanation:
A horizontal row on a periodic table is known as a period in a periodic table. Whereas vertical rows or columns represent groups in a periodic table.
For example, Li, Na, B, C, N, O are all second period elements.
On the other hand, O, S, Se, Te are all group 16 elements as they lie in column 16 of the periodic table.
Hence, we can conclude that a horizontal row on the periodic table is known as a period.
