## **Core Concept**
The protein efficiency ratio (PER) is a method used to evaluate the quality of a protein source. It is defined as the ratio of weight gain of the test subject (usually an animal) to the intake of a particular protein source. This measure helps in understanding how efficiently a protein supports growth.

## **Why the Correct Answer is Right**
The correct formula for calculating the Protein Efficiency Ratio is:
[ text{PER} = frac{text{Weight gain of animal (g)}}{text{Protein consumed (g)}} ]
This ratio essentially quantifies the gain in weight of the animal per gram of protein consumed, making it a direct measure of protein quality and its ability to support growth.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because it does not accurately represent the formula for PER. Without the specific details of the formula provided in the option, it's understood that PER is about the ratio of weight gain to protein intake, not some other calculation.
- **Option B:** Similarly, this option does not correctly represent the PER formula. It might be confusing the PER with another nutritional index or calculation.
- **Option D:** This option is also incorrect as it does not represent the correct formula for calculating the Protein Efficiency Ratio.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the Protein Efficiency Ratio is particularly useful in assessing the quality of dietary proteins, especially in the context of nutritional science and food technology. It's a straightforward yet valuable tool for comparing the nutritional value of different protein sources.

## **Correct Answer:** B. $frac{text{Gain in wt(g)}}{text{Protein intake(g)}}$