If $z$ and $\omega$ are two non-zero complex numbers such that $|z \omega|=1$ and $\operatorname{Arg} z-\operatorname{Arg} \omega=\frac{\pi}{2}$ then $\bar{z} \omega=$

• A

  $i$
• B

  $-1$
• C

  $1$
• Correct answer
  D

  $-i$

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