## Core Concept
The question pertains to the causes of non-union in femoral neck fractures, which is a significant complication in orthopedic trauma. Non-union in femoral neck fractures is often related to the disruption of the blood supply to the femoral head, leading to avascular necrosis and failure of fracture healing.

## Why the Correct Answer is Right
The correct answer, **. Disruption of blood supply**, is right because the blood supply to the femoral head is easily compromised in femoral neck fractures. The femoral head receives its blood supply mainly from the medial and lateral circumflex femoral arteries, which run along the surface of the femoral neck. When a fracture occurs, these vessels can be damaged or disrupted, leading to ischemia of the femoral head. This ischemia impairs the healing process, resulting in non-union or avascular necrosis.

## Why Each Wrong Option is Incorrect
- **Option A:** While infection (if it occurs) can certainly complicate fracture healing and lead to non-union, it is not the most common or direct cause of non-union in femoral neck fractures compared to disruption of blood supply.
- **Option B:** Inadequate immobilization can contribute to non-union in general, but femoral neck fractures are usually managed with stable internal fixation methods that minimize movement at the fracture site. Thus, inadequate immobilization is less directly related to non-union in this specific context.
- **Option C:** Poor nutrition can affect overall healing and bone health but is not as directly linked to the specific issue of non-union in femoral neck fractures as disruption of blood supply.

## Clinical Pearl / High-Yield Fact
A key point to remember is that the risk of non-union and avascular necrosis is higher in displaced femoral neck fractures than in non-displaced fractures. Prompt and accurate reduction and stable internal fixation are crucial in minimizing these risks.

## Correct Answer: . Disruption of blood supply