Which of the following is (are) spontaneous processes?(i)a ball rolling down a hill
(ii)a car rusting
(iii)the decomposition of water into H₂ gas and O₂ gas

• A. (i) only
• B. (ii) only
• C. (iii) only
• D. (i) and (ii) only
• E. (i), (ii), and (iii)

Answer: (D)

Verified step by step guidance

1. Understand the concept of spontaneity in chemistry: A spontaneous process is one that occurs naturally under given conditions without needing external energy input. It is often associated with an increase in entropy or a decrease in free energy.
2. Analyze process (i): A ball rolling down a hill is spontaneous because it moves from a position of higher potential energy to lower potential energy, driven by gravity, which is a natural force.
3. Analyze process (ii): A car rusting is spontaneous because it involves the oxidation of iron in the presence of oxygen and moisture, which is a natural and energetically favorable process.
4. Analyze process (iii): The decomposition of water into H2 gas and O2 gas is not spontaneous under normal conditions because it requires energy input to break the strong O-H bonds in water molecules. This process is typically achieved through electrolysis.
5. Conclude based on the analysis: Processes (i) and (ii) are spontaneous, while process (iii) is not spontaneous under normal conditions. Therefore, the correct answer is (i) and (ii) only.