Electronegativity increases across Period 3 due to rising effective nuclear charge.

Steps:

• Identify Period 3 elements: Na to Ar, moving left to right.
• Recall electronegativity trend: increases across a period as nuclear charge pulls electrons closer, reducing atomic radius.
• Expect graph: steady rise from low at Na (0.9) to high at Cl (3.0), with Ar similar or excluded.
• Match to options: select graph showing consistent upward trend.

Why B is correct:

• Depicts increasing electronegativity, aligning with Pauling's scale where effective nuclear charge dominates in the same period.

Why the others are wrong:

• A: Shows decrease, opposite to periodic trend.
• C: Irregular fluctuations, ignoring smooth nuclear charge effect.
• D: Flat line, contradicting radius shrinkage and charge increase.

Final answer: B