Due to which forces the air from outside move into the lungs
(i) An increase in pulmonary volume
(ii) Decrease the intra-pulmonary pressure
(iii) Reduction in thoracic volume

Options

A. i and ii
B. i, ii, iii
C. i and iii
D. ii, iii

Answer

To answer the question regarding the forces that cause air to move from outside into the lungs, we can break it down step by step:

### Step-by-Step Solution:

1. **Understanding Lung Mechanics**:
- The lungs have a natural tendency to collapse due to elastic recoil. Conversely, the thoracic cage tends to expand. These opposing forces help maintain the lungs in an inflated state.

2. **Role of Diaphragm and Intercostal Muscles**:
- During inhalation (inspiration), the diaphragm contracts and moves downward, while the external intercostal muscles contract to lift the rib cage. This action increases the volume of the thoracic cavity.

3. **Increase in Pulmonary Volume**:
- As the thoracic cavity expands, the volume of the lungs also increases. This is the first force that allows air to move into the lungs.

4. **Decrease in Intrapulmonary Pressure**:
- When the volume of the lungs increases, the pressure inside the lungs (intrapulmonary pressure) decreases. According to Boyle's Law, when the volume increases, the pressure decreases. This creates a pressure gradient where the atmospheric pressure (outside the body) is higher than the pressure inside the lungs, causing air to flow in.

5. **Reduction in Thoracic Volume**:
- This statement is incorrect. During inhalation, the thoracic volume actually increases, not decreases. A reduction in thoracic volume would lead to an increase in pressure, which would push air out of the lungs rather than drawing it in.

### Conclusion:
- The correct forces that allow air to move into the lungs are:
(i) An increase in pulmonary volume (correct)
(ii) A decrease in intrapulmonary pressure (correct)
(iii) A reduction in thoracic volume (incorrect)

Thus, the correct answers are (i) and (ii).