Assertion $A$: Barium is not required in the normal biochemical processes of the human body.
Reason $R$: Barium does not exhibit more than one oxidation state.

• A
  Both $A$ and $R$ are true and $R$ is the correct explanation of $A$.
• B
  Both $A$ and $R$ are true but $R$ is not the correct explanation of $A$.
• C
  $A$ is true but $R$ is false.
• D
  Both $A$ and $R$ are false.