$\mathrm{KO}_2$ is used in life supports in space crafts, submarines and emergency breathing apparatus since it

• A

  absorbs $\mathrm{CO}_2$
• B

  release $\mathrm{O}_2$
• C

  releases $\mathrm{CO}_2$
• Correct answer
  D

  absorbs $\mathrm{CO}_2$ and releases $\mathrm{O}_2$

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