Fill in the following blanks with suitable words :
Air _____ on heating and ______ on cooling .

Explanation

To fill in the blanks in the sentence "Air _____ on heating and ______ on cooling," we need to understand the behavior of air when it is subjected to changes in temperature.

### Step-by-Step Solution:

1. **Understanding the Properties of Air:**
- Air is a mixture of gases, primarily nitrogen and oxygen. Like all gases, air has specific properties when it comes to temperature changes.

2. **Effect of Heating on Air:**
- When air is heated, the molecules gain energy and move faster. This increased movement causes the air to take up more space, which is known as expansion.

3. **Effect of Cooling on Air:**
- Conversely, when air cools down, the molecules lose energy and move slower. This decrease in movement causes the air to occupy less space, which is known as contraction.

4. **Filling in the Blanks:**
- Based on the properties discussed, we can fill in the blanks:
- The first blank should be filled with "expands" (Air expands on heating).
- The second blank should be filled with "contracts" (Air contracts on cooling).

5. **Final Sentence:**
- Therefore, the complete sentence is: "Air expands on heating and contracts on cooling."

### Final Answer:
Air **expands** on heating and **contracts** on cooling.

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