NaX (Sodium salt of particular anion 'X') gives brisk effervescence of Y with dilute HCl. On heating, NaX evolves gas Y which can be completely absorbed in conc. KOH solution and is colorless odourless gas. Hence X and Y respectively are :

Options

A. `HSO_(3)^(-), SO_(2)`
B. `HS^(-) & H_(2)S`
C. `HCO_(3)^(-), CO_(2)`
D. `HC_(2)O_(4)^(-) &CO_(2)+CO`s

Explanation

To solve the problem, we need to identify the anion 'X' and the gas 'Y' based on the information provided. Let's break it down step by step.

### Step 1: Analyze the given information
We have a sodium salt NaX, which produces a gas Y when it reacts with dilute HCl. Additionally, when NaX is heated, it also evolves gas Y, which is colorless, odorless, and can be absorbed by concentrated KOH solution.

**Hint:** Focus on the properties of the gases produced and their reactions with KOH.

### Step 2: Identify the possible gases
The gas Y must be colorless and odorless, and it should be completely absorbed by concentrated KOH. Common gases that fit these criteria include carbon dioxide (CO2) and ammonia (NH3). However, ammonia has a distinct smell, so it cannot be the gas we are looking for.

**Hint:** Consider the properties of common gases and their reactions with KOH.

### Step 3: Consider the reaction with dilute HCl
When NaX reacts with dilute HCl, it produces gas Y. If we consider NaHCO3 (sodium bicarbonate), the reaction with HCl is as follows:
\[ \text{NaHCO}_3 + \text{HCl} \rightarrow \text{NaCl} + \text{H}_2\text{O} + \text{CO}_2 \uparrow \]

This reaction produces CO2, which is a colorless and odorless gas.

**Hint:** Look for a sodium salt that produces CO2 when reacting with acids.

### Step 4: Analyze the heating of NaX
When NaHCO3 is heated, it decomposes to form:
\[ \text{2 NaHCO}_3 \rightarrow \text{Na}_2\text{CO}_3 + \text{H}_2\text{O} + \text{CO}_2 \uparrow \]

Again, CO2 is evolved, which matches the criteria for gas Y.

**Hint:** Consider thermal decomposition reactions of sodium salts.

### Step 5: Conclusion
From the analysis, we can conclude that:
- The anion X is bicarbonate, \( \text{HCO}_3^- \).
- The gas Y is carbon dioxide, \( \text{CO}_2 \).

Thus, X and Y respectively are:
**X = HCO3^- and Y = CO2.**

### Final Answer:
X = HCO3^- (bicarbonate ion) and Y = CO2 (carbon dioxide).

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