Which of the following statements is correct regarding the property of lanthanoid contraction?

💡 Solution & Explanation

The steady decrease in atomic and ionic radii across the lanthanoid series is known as lanthanoid contraction, which is fundamentally caused by the poor shielding effect of the 4f electrons that allows the nuclear charge to pull the outer electrons closer. Alternative choices suggesting an increase in atomic radii or a sudden density jump misrepresent fundamental periodic trends. Understanding lanthanoid contraction is crucial for explaining why zirconium and hafnium exhibit nearly identical chemical properties.