There are two closely named iodine-based titrations: iodimetry and iodometry. They sound alike but work differently, and the question is testing whether you can tell them apart.
Step 1: Understand iodometry vs iodimetry. These two terms are often confused. The question asks about iodometric titration specifically, so it is important to get the definition right.
Step 2: What is iodimetry (direct titration)? Iodimetry uses iodine (I2) directly as the titrant in a burette to titrate a reducing substance. Iodine is added directly to the analyte. This is a direct titration.
Step 3: What is iodometry (indirect titration)? Iodometry is an indirect method. An oxidizing agent in the sample reacts with excess potassium iodide (KI) to liberate iodine. The amount of iodine liberated is then titrated with sodium thiosulfate using starch as the indicator. The sample is never directly titrated with iodine.
Step 4: Rule out the wrong options. Option 1 (direct titration with iodine) describes iodimetry, not iodometry. Option 3 (acid-base) and Option 4 (precipitation) are completely different types of reactions.
Step 5: Confirm the correct answer. Iodometric titration is an indirect method: the analyte (an oxidant) reacts with KI to release iodine, which is then measured. This matches Option 2.
Answer: Option (2) — Indirect titration using iodine