What are the horizontal rows on the periodic table called?

• A. Families
• B. Blocks
• C. Periods
• D. Groups

Answer: (C)

Verified step by step guidance

1. Understand that the periodic table is organized in two main directions: horizontally and vertically.
2. Recognize that the vertical columns are called 'Groups' or 'Families', which contain elements with similar chemical properties.
3. Identify that the horizontal rows are called 'Periods'. Each period represents elements with increasing atomic number from left to right.
4. Note that 'Blocks' refer to sections of the periodic table based on electron configurations (s, p, d, f blocks), not rows or columns.
5. Therefore, the correct term for the horizontal rows on the periodic table is 'Periods'.