Which of the following statements is incorrect with reference to $Ce$ $(Z=58)$?

• A
  Atomic size of $Ce$ is more than that of $Lu$.
• B
  $Ce$ shows common oxidation states of $+3$ and $+4$.
• C
  $Ce^{4+}$ is a reducing agent.
• D
  $Ce$ in $+3$ oxidation state is more stable than in $+4$.