Respiratory volumes:
Respiratory volumes refer to the different amounts of air that can be inhaled, exhaled, or held within the lungs during different phases of breathing. These volumes are important indicators of lung function and can be measured using a spirometer.

Vital capacity:
Vital capacity is the maximum amount of air that can be exhaled after a maximum inhalation. It is the sum of three respiratory volumes: tidal volume (TV), expiratory reserve volume (ERV), and inspiratory reserve volume (IRV). Vital capacity represents the total amount of air that can be exchanged in a breath and is an important measure of lung function.

Total lung capacity:
Total lung capacity is the maximum amount of air that the lungs can hold. It is the sum of four respiratory volumes: tidal volume (TV), inspiratory reserve volume (IRV), expiratory reserve volume (ERV), and residual volume (RV). Total lung capacity includes both the air that can be exchanged during breathing (vital capacity) and the air that remains in the lungs after maximum exhalation (residual volume).

Residual volume:
Residual volume is the volume of air that remains in the lungs after maximum exhalation. It cannot be measured directly using a spirometer and is estimated using other techniques. Residual volume is important because it ensures that the lungs do not completely collapse between breaths and allows for continuous gas exchange.

Correct option:
The correct option is B. Vital capacity of lungs = Total lung capacity - Residual air. This means that the vital capacity of the lungs is equal to the total lung capacity minus the residual volume. This equation represents the relationship between vital capacity and total lung capacity, taking into account the air that remains in the lungs after maximum exhalation.

Explanation:
The vital capacity represents the maximum amount of air that can be exchanged during breathing, while the total lung capacity represents the maximum amount of air that the lungs can hold. Since the residual volume represents the air that remains in the lungs after maximum exhalation, subtracting it from the total lung capacity gives us the vital capacity.

In summary, the correct option B states that the vital capacity of the lungs is equal to the total lung capacity minus the residual volume. This equation accurately represents the relationship between these respiratory volumes.

Vital capacity of lungs is the maximum volume of air a person can breathe in after forced expiration. This includes ERV, TV, and IRV or the maximum volume of air a person can breathe out after a forced inspiration.