Identify the properties, uses, and methods of separation and identification of common gases based on their reactions and physical properties.

The previous setup (Question 26) showed oxygen collected over water. This method is used for gases that are insoluble or sparingly soluble in water.
26. (b) Property: $\boxed{\text{Slightly soluble in water}}$

Oxygen is essential for many processes.
26. (c) Use: $\boxed{\text{Respiration}}$ (or combustion, welding, medical use, etc.)

From the table:

• Gas X reacts with $H_2SO_4$.
• Gas Y is not affected by $H_2SO_4$. To separate them, pass the mixture through concentrated sulphuric acid. Gas X will react and be absorbed, while gas Y will pass through unaffected. 27. (a) Method: Pass the mixture of gases X and Y through concentrated sulphuric acid. Gas X will react and be absorbed, leaving gas Y to be collected.

From the table:

• Gas X is lighter than air.
• Gas X reacts with $H_2SO_4$ to form a salt (meaning it's a basic gas).
• Gas X dissolves without reacting in $NaOH$. Ammonia ($NH_3$) fits these properties. It is lighter than air (molar mass 17 g/mol), is a basic gas that reacts with acids to form salts, and dissolves in aqueous solutions like NaOH without reacting with the base itself. 27. (b) Identity and Reason: $\boxed{\text{Ammonia (NH}_3\text{)}}$. It is lighter than air and reacts with acids to form salts.

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