A student heats an unknown organic compound and a gas is released. This gas turns lime water milky but does not support combustion. Which of the following is the gas?

1. A

   Oxygen

2. B

   Carbon dioxide

3. C

   Methane

4. D

   Hydrogen

Appeared in: RRB Nsg. Superintendent -29 April-2025 (shift-2nd)

Explanation

• Carbon dioxide is uniquely identified by its characteristic reaction with lime water (calcium hydroxide solution), turning it milky due to the formation of insoluble calcium carbonate.
• It is a non-combustible gas and does not support combustion, a property utilized in fire extinguishers.
• The heating of many organic compounds results in decomposition that produces carbon dioxide and water.

Why Other Options Were Wrong

• Option A: Oxygen is incorrect because it supports combustion; it does not extinguish it.
• Option C: Methane is incorrect because it is a combustible gas (it burns) and does not have any reaction with lime water.
• Option D: Hydrogen is incorrect because it is a highly combustible gas that burns with a characteristic 'pop' sound and does not affect lime water.

Related Visual

• Visual 1: Diagram: An illustration of the experimental setup for the lime water test, showing gas from a reaction bubbling through a test tube of clear lime water, causing it to turn cloudy.
• Visual 2: Infographic: A comparative table showing the key properties (color, odor, combustibility, lime water test) of common laboratory gases like Carbon Dioxide, Oxygen, Hydrogen, and Methane.

Clinical Relevance

• Nursing practice connection: Knowing Identification of gases based on chemical properties helps nurses interpret findings accurately and avoid errors in routine assessment, medication administration, and patient teaching.
• While this is a basic chemistry question, understanding gas properties is fundamental in nursing. Carbon dioxide (CO₂) is a major waste product of cellular respiration, and its levels in the blood are critical for maintaining acid-base balance (pH).
• Oxygen (O₂) is essential for life and is administered as a primary medical intervention (oxygen therapy) for patients with hypoxia or respiratory distress.
• Knowledge of combustible gases like methane and hydrogen is important for safety awareness in both hospital and home environments, especially concerning leaks from medical equipment or utility lines.

How to Approach the Question

• First, break down the question to identify the two key properties of the unknown gas: 1) it turns lime water milky, and 2) it does not support combustion.
• Next, evaluate each option against these two properties.
• Consider Oxygen: It supports combustion, which contradicts the second property. Eliminate this option.
• Consider Carbon dioxide: Recall the classic test for CO₂ is that it turns lime water milky. It is also known to be non-combustible. This option matches both properties.
• Consider Methane and Hydrogen: Both are known to be combustible fuels, which contradicts the second property. Eliminate these options.
• Conclude that Carbon dioxide is the only gas that fits both descriptions provided in the question.

Concept Tested & Keywords

• Concept Tested: Identification of gases based on chemical properties
• Stem keywords: gas released, turns lime water milky, does not support combustion
• Lead-in keywords: Which of the following

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Qn9Hk62UfGviffuiPju9Oh

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