**Core Concept**
The concept of ideal protein refers to a protein source that provides all essential amino acids (EAAs) in sufficient quantities to support human growth and maintenance. This is crucial for protein synthesis, repair, and overall health.

**Why the Correct Answer is Right**
Egg is considered an ideal protein source due to its high biological efficiency and nitrogen-poor utilization (NPU). The NPU is a measure of the proportion of ingested nitrogen that is retained by the body. Eggs have a high NPU value, indicating that they are efficiently utilized by the body for protein synthesis. Additionally, eggs contain all essential amino acids, with a balanced ratio that makes them easily absorbed and utilized by the body.

**Why Each Wrong Option is Incorrect**
**Option A:** High cholesterol is a characteristic of eggs, but it is not the reason why egg is considered an ideal protein source. High cholesterol levels can actually be a concern for cardiovascular health.

**Option B:** While eggs do contain a significant amount of protein per 100 grams, this is not the primary reason why they are considered an ideal protein source. Other protein sources, such as meat and fish, also have high protein content.

**Option D:** Eggs do contain all essential amino acids, but this is not the reason why they are considered an ideal protein source. The limiting amino acid concept is relevant when considering plant-based protein sources, where one amino acid may be present in insufficient quantities.

**Clinical Pearl / High-Yield Fact**
A good rule of thumb is that animal-based protein sources, such as eggs, meat, and fish, are generally considered ideal protein sources due to their high NPU and balanced amino acid profiles. Plant-based protein sources, such as legumes and whole grains, can be ideal protein sources if consumed in combination to provide all essential amino acids.

**✓ Correct Answer: C. High biological efficiency and NPU**