Question

the size of an atom generally increases:
up a group and from right to left across a period.
down a group and from left to right across a period.
down a group and from right to left across a period.
up a group and from left to right across a period.
up a group and diagonally across the periodic table.

Explanation:

To determine how atomic size changes, we analyze periodic trends:

• Down a group: As we move down a group (vertical column), the number of electron shells increases. Each new shell is further from the nucleus, so atomic size (radius) increases.
• Across a period (left to right): As we move left to right across a period (horizontal row), the number of protons increases, pulling electrons closer to the nucleus (increased effective nuclear charge). Thus, atomic size decreases (so size increases from right to left across a period).

Matching these trends: "down a group and from right to left across a period" is correct.

Answer:

C. down a group and from right to left across a period. (Note: Assuming the options are labeled A - E, the third option is the correct one. If original labels differ, adjust to the option text: "down a group and from right to left across a period".)