Final answer:
Electronegativity decreases within a group due to increased atomic size and increases across a period due to a higher nuclear charge. The correct answer to the trend in electronegativity is C) Electronegativity decreases within a group and increases within a period.
Step-by-step explanation:
The trend in electronegativity within a group on the periodic table is that it decreases from top to bottom. This decrease is due to the increase in atomic size, which makes the nucleus less effective in pulling the bonding electrons. On the other hand, as we move across a period from left to right, the electronegativity tends to increase. This increase is associated with a decrease in atomic size and an increase in nuclear charge, enabling the nucleus to pull the bonding electron pair closer to itself more effectively.
Considering the options provided:
- A) Incorrect, because electronegativity does not increase within a group.
- B) Incorrect, because electronegativity decreases within a group.
- C) Correct, because electronegativity decreases within a group and increases within a period.
- D) Incorrect, because electronegativity does not decrease across a period.
Therefore, the answer to the question is C) Electronegativity decreases within a group and increases within a period.