**Core Concept**
HbA2 is a minor component of hemoglobin in adults, making up approximately 2-3.5% of total hemoglobin. It is a variant of the alpha-globin chain, differing from the more common alpha-globin chain by a single amino acid substitution.

**Why the Correct Answer is Right**
HbA2 is produced during fetal development and persists in small amounts throughout adulthood. It is composed of two alpha-globin chains and two delta-globin chains. The presence of HbA2 is a normal finding in adults but can be elevated in certain conditions, such as beta-thalassemia minor. The delta-globin chains in HbA2 are more prone to oxidation than alpha-globin chains, making HbA2 more susceptible to denaturation and breakdown.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not accurately describe the composition of HbA2, which contains delta-globin chains, not beta-globin chains.
**Option B:** This option is incorrect because it incorrectly states that HbA2 is a major component of hemoglobin in adults, when in fact it makes up only a small percentage of total hemoglobin.
**Option C:** This option is incorrect because it does not accurately describe the normal range of HbA2 levels in adults, which typically range from 2-3.5%.

**Clinical Pearl / High-Yield Fact**
It is essential for clinicians to recognize the normal range of HbA2 levels in adults, as elevated levels can be a diagnostic clue for beta-thalassemia minor. A mnemonic to remember the normal range is "2-3.5% is what you see in healthy adults, but beware of beta-thalassemia when it's higher!"

**Correct Answer: C. 2-3.5% of total hemoglobin.**