$STATEMENT-1$: In water,orthoboric acid behaves as a weak monobasic acid. because
$STATEMENT-2$: In water,orthoboric acid acts as a proton donor.

• A
  $Statement-1$ is True,$Statement-2$ is True; $Statement-2$ is a correct explanation for $Statement-1$.
• B
  $Statement-1$ is True,$Statement-2$ is True; $Statement-2$ is $NOT$ a correct explanation for $Statement-1$.
• C
  $Statement-1$ is True,$Statement-2$ is False.
• D
  $Statement-1$ is False,$Statement-2$ is True.