**Core Concept**
Tetralogy of Fallot (TOF) is a congenital heart defect characterized by four key components: ventricular septal defect (VSD), pulmonary stenosis, right ventricular hypertrophy, and an overriding aorta. This condition leads to cyanosis due to decreased blood flow to the lungs and subsequent mixing of oxygenated and deoxygenated blood.

**Why the Correct Answer is Right**
The child's cyanotic spells are likely due to the decreased pulmonary blood flow and subsequent right-to-left shunting through the VSD. The chest X-ray would show a "boot-shaped" heart, which is a classic radiographic feature of TOF. This is caused by the right ventricular hypertrophy, which gives the heart a characteristic shape. The X-ray would also show decreased pulmonary vascular markings, consistent with decreased pulmonary blood flow.

**Why Each Wrong Option is Incorrect**
**Option B:** Tricuspid atresia is a different congenital heart defect where the tricuspid valve is absent or abnormally developed. This condition would lead to decreased blood flow to the right ventricle and subsequent cyanosis, but the characteristic "boot-shaped" heart and decreased pulmonary vascular markings on the chest X-ray are not typical of tricuspid atresia.

**Option C:** Pulmonary atresia with intact ventricular septum is a condition where the pulmonary valve is completely blocked, leading to decreased blood flow to the lungs. However, this condition would not cause the characteristic "boot-shaped" heart seen in TOF.

**Option D:** Total Anomalous Pulmonary Venous Connection (TAPVC) is a congenital heart defect where the pulmonary veins are connected to the systemic veins rather than the left atrium. This condition would lead to increased pulmonary blood flow and subsequent pulmonary congestion, which is not consistent with the decreased pulmonary vascular markings seen in TOF.

**Clinical Pearl / High-Yield Fact**
The "boot-shaped" heart is a classic radiographic feature of Tetralogy of Fallot and should be remembered by students as a key diagnostic clue. This characteristic shape is due to the right ventricular hypertrophy and is a critical differentiator from other congenital heart defects.

**✓ Correct Answer: A. Tetralogy of Fallot**