The venous blood in the lung has a `PCO_2` of 46 mm Hg. Should the alveolar `PCO_2` exceed or be less than 46 mm Hg to result in diffusion of `CO_2` from the blood into alveolus?

Explanation

To determine whether the alveolar partial pressure of carbon dioxide (PCO₂) should exceed or be less than 46 mm Hg for diffusion of CO₂ from the blood into the alveolus, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Concept of Diffusion**:
- Diffusion is the movement of gas from an area of higher concentration to an area of lower concentration. In terms of partial pressure, this means that gas will move from a region of higher partial pressure to a region of lower partial pressure.

2. **Identify the Given Values**:
...