**Core Concept**
In a healthy individual, arterial oxygen saturation is a key indicator of oxygen delivery to tissues. SpO₂ (saturation of oxygen in arterial blood) reflects the percentage of hemoglobin bound to oxygen and is closely linked to alveolar gas exchange and pulmonary function.

**Why the Correct Answer is Right**
A normal arterial oxygen saturation is generally considered satisfactory when SpO₂ is ≥90%. This threshold ensures adequate oxygenation of hemoglobin, preventing hypoxemia and maintaining tissue oxygenation. Values below 90% may indicate respiratory or cardiovascular compromise, even if the patient is asymptomatic. The standard clinical benchmark for normal oxygen saturation is set at 90–100%, with 90% being the minimum acceptable level in healthy individuals.

**Why Each Wrong Option is Incorrect**
Option A: 80 – This is dangerously low and indicates severe hypoxemia, commonly seen in respiratory failure or pulmonary disease, not normal health.
Option B: 85 – This is below the normal threshold and may suggest mild hypoxemia, not a satisfactory level in healthy individuals.
Option D: Any of the above – Incorrect because only 90% meets the accepted standard for normal oxygen saturation; lower values are not considered satisfactory.

**Clinical Pearl / High-Yield Fact**
In clinical practice, SpO₂ ≥90% is the accepted normal limit in healthy adults. Values below 90% warrant investigation for respiratory or cardiovascular causes, especially in patients with symptoms like dyspnea or fatigue.

✓ Correct Answer: C. 90