🔍 Key Concepts

• Orsat apparatus and its purpose in flue gas analysis • Typical absorbents used for carbon dioxide (CO₂), oxygen (O₂), and carbon monoxide (CO) in classical gas analysis • Chemical property needed: a solution that strongly absorbs acidic gas CO₂

💭 Think About

• First, recall which gas each absorbent is usually assigned to in the standard three‑bottle Orsat setup: one bottle for CO₂, one for O₂, and one for CO. • Think about which of the listed chemicals is a strong alkali that would readily combine with an acidic oxide like CO₂ to form a carbonate. • Separate in your mind which reagents are used for oxygen absorption versus carbon monoxide absorption—then see which remaining option matches CO₂.

✅ Before You Answer

• Identify which option is a strong base/alkali that would react with CO₂ to form a carbonate or bicarbonate. • Recall which reagent is classically paired with oxygen (O₂) absorption in an alkaline solution and which is paired with carbon monoxide (CO) via complex formation. • Ensure you are not mixing up the reagent normally used for O₂ with that used for CO₂ in the Orsat apparatus.