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JEE Advanced levelSingle correct optionDifficulty 3 of 3df212

Assertion (A): Early actinoids (Pa to Pu) show many oxidation states, but from Cm onwards the +3 state predominates. Reason (R): With increasing nuclear charge the orbitals are progressively stabilised and become less available for bonding. Choose the correct option.

  1. ABoth A and R are true and R is the correct explanation of A
  2. BBoth A and R are true but R is not the correct explanation of A
  3. CA is true but R is false
  4. DA is false but R is true

Answer: A

Across the series Zeff on the electrons rises (poor shielding), so energies drop below /. Late actinoids therefore use mainly the / electrons, giving +3, in contrast with the many states of the early members. R correctly explains A.
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