Which of the following processes shows a decrease in entropy of the system?

• A. NaClO₃(s) → Na⁺(aq) + ClO₃^–(aq)
• B. CH₃OH(l) → CO(g) + 2 H₂(g)
• C. H₂O(l) → H₂O(g)
• D. 2 NO(g) + O₂(g) → 2 NO₂(g)
• E. COCl₂(g) → CO(g) + Cl₂(g)

Answer: (D)

Verified step by step guidance

1. Understand the concept of entropy: Entropy is a measure of the disorder or randomness in a system. Generally, processes that increase the number of gas molecules or increase the freedom of movement of particles result in an increase in entropy.
2. Analyze each process: For each chemical reaction, consider the states of the reactants and products. Solid to aqueous, liquid to gas, and decomposition reactions typically increase entropy, while reactions that form fewer gas molecules or more ordered states decrease entropy.
3. Evaluate the first process: NaClO3(s) → Na+(aq) + ClO3–(aq). This process involves dissolving a solid into ions in solution, which increases disorder, thus increasing entropy.
4. Evaluate the second process: CH3OH(l) → CO(g) + 2 H2(g). This decomposition reaction increases the number of gas molecules, leading to an increase in entropy.
5. Evaluate the correct answer: 2 NO(g) + O2(g) → 2 NO2(g). This reaction involves combining gases to form fewer gas molecules, which decreases the disorder and thus decreases entropy.