Question

which of the following explains why electronegativity decreases from right to left across a period?
a the number of electrons decreases, and electrons attract each other
b the number of protons decreases, so the nucleus is less positively charged
c the atomic radius decreases, so electrons are more strongly pulled
d the number of neutrons decreases, so the nucleus is less positively charged
e the nucleus becomes lighter, so electrons are less strongly attracted

Explanation:

To determine why electronegativity decreases from right to left across a period, we analyze each option:

• Option a: Electrons repel each other, and the number of electrons changing isn't the main reason for electronegativity change here. Eliminate a.
• Option b: As we move left across a period, the atomic number (number of protons) decreases. A less positively charged nucleus has a weaker pull on electrons, which lowers electronegativity. This matches the trend.
• Option c: Atomic radius increases (not decreases) from right to left across a period, and a larger radius would mean weaker electron pull, so this is incorrect. Eliminate c.
• Option d: Neutrons don't affect the positive charge of the nucleus (protons do), so this is irrelevant. Eliminate d.
• Option e: The "lightness" of the nucleus isn't the key factor; it's the positive charge from protons. Eliminate e.

Answer:

b. The number of protons decreases, so the nucleus is less positively charged