Identify the reaction/process in which the entropy decreases

• Correct answer
  A

  $\mathrm{H}_2 \mathrm{O}$ (l) $\longrightarrow \mathrm{H}_2 \mathrm{O}$ (s)
• B

  $\mathrm{H}_2 \mathrm{O}$ (l) $\longrightarrow \mathrm{H}_2 \mathrm{O}$ (g)
• C

  $\mathrm{H}_2 \mathrm{O}(\mathrm{g}) \longrightarrow 2 \mathrm{H}(\mathrm{g})$
• D

  Crystal $(100 \mathrm{~K}) \longrightarrow$ Crystal $(200 \mathrm{~K})$

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