See image — Haloalkanes and Haloarenes Chemistry Question

💡 Solution & Explanation

Concept: The rate-determining step (RDS) is the slowest step in a multi-step reaction mechanism. On an energy profile diagram, the slowest step corresponds to the step with the highest activation energy (Ea), which is the energy difference between the reactant of that step and the transition state of that step. Reasoning: In the given energy profile diagram, there are three steps: - Step 1: A --> B, with transition state 1 (peak 1, the highest overall peak) - Step 2: B --> C, with transition state 2 (peak 2) - Step 3: C --> D, with transition state 3 (peak 3) To find the activation energy for each step, we measure the energy difference between the starting point of each step and its respective transition state: - Ea(step 1): Energy from A up to peak 1 — this is the largest barrier because peak 1 is the highest point on the diagram and A is at a relatively low energy. - Ea(step 2): Energy from intermediate B up to peak 2 — smaller than Ea(step 1) because peak 2 is lower than peak 1. - Ea(step 3): Energy from intermediate C up to peak 3 — smallest barrier. From the diagram, peak 1 (transition state 1) is clearly the highest point, and the energy of A is lower than intermediates B and C. Therefore, the activation energy for Step 1 (A --> B) is the largest, making it the slowest and hence the rate-determining step. Why other options fail: - (b) B --> C: The activation energy from B to peak 2 is smaller than that of step 1. - (c) C --> D: The activation energy from C to peak 3 is the smallest of all three steps. - (d) can not predict: We can predict the RDS from the diagram; it is clearly step 1. Therefore, the correct answer is A.