**Core Concept**
Beta thalassemia is a genetic disorder affecting the production of the beta-globin chains of hemoglobin, leading to various clinical manifestations and laboratory findings. Accurate diagnosis of beta thalassemia is crucial for appropriate management and genetic counseling.

**Why the Correct Answer is Right**
Hemoglobin (Hb) electrophoresis is a definitive diagnostic tool for identifying and quantifying the different types of hemoglobin present in a patient's blood. In beta thalassemia, Hb electrophoresis reveals reduced or absent production of beta-globin chains, leading to increased levels of alpha-globin chains and formation of abnormal hemoglobins such as Hb Bart's, Hb Portland, or Hb A2. This test is particularly useful for distinguishing between beta thalassemia major and minor, as well as for identifying carriers of the beta thalassemia gene.

**Why Each Wrong Option is Incorrect**
**Option A:** The NESTROFT (Naked Eye Single Tube Red Cell Osmotic Fragility Test) test is used to diagnose hereditary spherocytosis, not beta thalassemia. It measures the osmotic fragility of red blood cells.
**Option B:** Hb A1c estimation is used to diagnose and monitor diabetes mellitus, not beta thalassemia. It measures the average blood glucose levels over the preceding 2-3 months.
**Option D:** Target cells in peripheral smear are a characteristic finding in beta thalassemia, but they are not specific to this condition and can be seen in other hemoglobinopathies or anemias. While they may suggest the presence of beta thalassemia, they are not sufficient for a definitive diagnosis.

**Clinical Pearl / High-Yield Fact**
Beta thalassemia major, also known as Cooley's anemia, is a severe form of beta thalassemia that requires regular blood transfusions to prevent complications such as anemia, heart failure, and bone deformities. Genetic counseling is essential for families affected by beta thalassemia to prevent the transmission of the disease to future generations.

**✓ Correct Answer: C. Hb electrophoresis**