The temperature should the hydrogen at $327 °\mathrm{C}$ be cooled at constant pressure so that the root mean square velocity of its molecules becomes half of its previous value is

• Correct answer
  A

  $-123 °\mathrm{C}$
• B

  $123 °\mathrm{C}$
• C

  $-100 °\mathrm{C}$
• D

  $0 °\mathrm{C}$

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