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Question 75

A freshly cut alkali metal starts bright but soon becomes dull in ordinary air. What best explains this family-specific observation?

  1. The metal changes into a gas at once.
  2. Its exposed surface reacts rapidly with air.Bonne réponse
  3. The interior permanently loses all metallic properties.
  4. Air polishes the surface into a dull layer.

Explication

The exposed surface rapidly reacts with substances in air, creating a tarnished layer that hides the metallic shine. Permanent brightness would imply little surface reaction and contradict the quick change that was observed.

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Question 75: A freshly cut alkali metal starts bright but soon becomes… · The Periodic Table and Elements · Questena