Which of the following statements is/are true?
a) The rusting of iron by oxygen is a non-spontaneous reaction.
b) The addition of a catalyst to a reaction increases spontaneity.
c) The movement of heat from a cold object to a hot object is a non-spontaneous reaction.
d) The diffusion of perfume molecules from one side of a room to the other is a non-spontaneous reaction.
e) None of the above. 

• A. C
• B. A,C
• C. D
• D. B,C

Answer: (A)

Verified step by step guidance

1. Step 1: Understand the concept of spontaneity in chemical reactions. A spontaneous reaction is one that occurs naturally under given conditions without external intervention. It is often associated with a negative Gibbs free energy change (ΔG < 0).
2. Step 2: Evaluate statement (a): The rusting of iron by oxygen is a spontaneous reaction. Rusting is a natural process that occurs when iron reacts with oxygen in the presence of moisture, leading to the formation of iron oxide. This process is thermodynamically favorable and spontaneous.
3. Step 3: Evaluate statement (b): The addition of a catalyst to a reaction does not affect the spontaneity of the reaction. Catalysts speed up the rate of a reaction by lowering the activation energy but do not change the Gibbs free energy of the reaction, thus not affecting spontaneity.
4. Step 4: Evaluate statement (c): The movement of heat from a cold object to a hot object is non-spontaneous. According to the second law of thermodynamics, heat naturally flows from hot to cold, making the reverse process non-spontaneous without external work.
5. Step 5: Evaluate statement (d): The diffusion of perfume molecules from one side of a room to the other is a spontaneous process. Diffusion occurs naturally as molecules move from an area of higher concentration to an area of lower concentration, driven by entropy increase.