Across the first transition series from scandium to zinc, the atomic radius

  • A. increases sharply
  • B. decreases sharply
  • C. changes very little, because the added d electrons shield the increased nuclear charge well
  • D. first increases then decreases sharply

Explanation

Each element adds a proton and a d electron, and because that electron enters an inner subshell it shields the outer 4s electrons effectively, so the net attraction on them barely changes. This near constancy is what makes transition metals so readily interchangeable in alloys. The contrast with the sharp contraction across a p block period is the point of the question.

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