The COD of water sample is determined using

• Correct answer
  A

  $50 \% \mathrm{H}_2 \mathrm{SO}_4, \mathrm{~K}_2 \mathrm{Cr}_2 \mathrm{O}_7$
• B

  $50 \% \mathrm{NaOH}, \mathrm{K}_2 \mathrm{Cr}_2 \mathrm{O}_7$
• C

  $50 \% \mathrm{CH}_3 \mathrm{COOH}, \mathrm{KMnO}_4$
• D

  $50 \% \mathrm{H}_2 \mathrm{SO}_4, \mathrm{FeSO}_4$

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