**Core Concept**
Tidal volume (TV) is the volume of air inhaled or exhaled during normal, relaxed breathing. It represents the amount of air that moves in and out of the lungs with each respiratory cycle.

**Why the Correct Answer is Right**
Tidal volume is approximately 500 milliliters (ml) in an average adult at rest. This volume is maintained by the balance between the elastic recoil of the lungs and the inward pull of the chest wall, as well as the outward pull of the diaphragm and other accessory muscles of respiration. The size of the tidal volume can increase with physical activity or stress, leading to an increase in minute ventilation.

**Why Each Wrong Option is Incorrect**
**Option A:** 100 ml - This is too low to be considered a normal tidal volume, as even infants and young children have a higher tidal volume than this.
**Option B:** 2000 ml - This is too high and would represent a large inspiratory effort, possibly seen in hyperventilation or during strenuous exercise.
**Option C:** 1000 ml - This is still higher than the average tidal volume and might be seen in individuals with respiratory disease or during exercise.

**Clinical Pearl / High-Yield Fact**
A decrease in tidal volume, known as hypopnea, can be an important indicator of respiratory compromise, such as in the case of respiratory failure or chronic obstructive pulmonary disease (COPD).

**Correct Answer: C. 500 ml**