Скачать или смотреть CSCA Chemistry MCQ: Gas Collected by Downward Displacement of Water

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Collection of gases is a very common and high-scoring topic in chemistry exams such as CSCA, SSC, HSC, and other competitive admission tests.

In this video, we solve an important CSCA Chemistry Mock Examination MCQ:

“Which gas is collected by downward displacement of water due to its low solubility?”

This question checks your understanding of gas collection methods, solubility of gases in water, and basic laboratory techniques.

🔬 Correct Concept Explained (Exam-Oriented)

Some gases are collected by downward displacement of water because they are almost insoluble or very slightly soluble in water. Such gases do not dissolve significantly and can safely be collected over water.

✔ Correct Answer: Oxygen (O₂)

Oxygen gas has low solubility in water, which makes it suitable for collection by downward displacement of water.

🧪 Why Oxygen Is Collected This Way

Oxygen is slightly soluble in water

It does not react with water

Collection over water is safe and efficient

This method is commonly used in laboratories

❌ Why Other Options Are Incorrect

HCl (Hydrogen chloride) → Highly soluble in water

NH₃ (Ammonia) → Extremely soluble in water

SO₂ (Sulfur dioxide) → Highly soluble in water

Because these gases dissolve readily in water, they cannot be collected by downward displacement of water.

🎯 Who Should Watch This Video?

CSCA exam candidates

SSC & HSC Chemistry students

Admission test aspirants

Students learning laboratory methods of gas collection

Anyone confused about solubility-based gas collection

📌 Exam Shortcut Tip

If the question mentions:

Downward displacement of water

Low solubility in water

👉 Answer is usually: Oxygen (O₂)

👍 Support & Engagement

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