The correct answer for the easily digestible source of protein is option 1, Egg albumin. Egg albumin is the clear liquid part of an egg, commonly known as egg white. It is considered a high-quality, complete protein as it contains all the essential amino acids required by the human body.

Egg albumin is often praised for its excellent digestibility. It is easily broken down by enzymes in the stomach and small intestine, making it readily absorbed and utilized by the body. This ease of digestion is particularly beneficial for individuals with digestive issues or those who need quick absorption of protein, such as athletes or people recovering from illness or surgery.

Option 2, Soybean, is also a good source of protein, but it is not as easily digestible as egg albumin. Soy protein contains anti-nutritional factors like trypsin inhibitors and phytic acid, which can affect digestion and absorption in some individuals.

Option 3, Fish flesh, is a good source of protein and is generally considered easily digestible. However, it may not be as universally digestible as egg albumin, as some individuals may have difficulty digesting certain types of fish or seafood.

Option 4, Red meat, is also a source of protein but is