Let $P$ be the set of all non-singular matrices of order 3 over $R$ and $Q$ be the set of all orthogonal matrices of order 3 over $R .$ Then,

• A

  $P$ is proper subset of $Q$
• Correct answer
  B

  $Q$ is proper subset of $P$
• C

  Neither $P$ is proper subset of $Q$ nor $Q$ is proper subset of $P$
• D

  $P \cap Q=\phi$, the void set

Hence, the correct answer is option: 'B'.