The formula of penta aquanitrato chromium (III) nitrate is,

• Correct answer
  A

  \( \left[\mathrm{Cr}\left(\mathrm{H}_{2} \mathrm{O}\right)_{5}\left(\mathrm{NO}_{3}\right)\right]\left(\mathrm{NO}_{3}\right)_{2} \)
• B

  \( \left[\mathrm{Cr}\left(\mathrm{H}_{2} \mathrm{O}\right)_{5}\left(\mathrm{NO}_{2}\right)\right] \mathrm{NO}_{3} \)
• C

  \( \left[\mathrm{Cr}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]\left(\mathrm{NO}_{3}\right)_{3} \)
• D

  \( \left[\mathrm{Cr}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]\left(\mathrm{NO}_{2}\right)_{2} \)

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