## **Core Concept**
The Body Mass Index (BMI) is a widely used tool to categorize individuals into various weight categories, including underweight, normal weight, overweight, and obesity. BMI is calculated as body mass (in kilograms) divided by the square of the person's height (in meters). The World Health Organization (WHO) has established BMI categories to classify adults.

## **Why the Correct Answer is Right**
The correct classification for obesity, according to the World Health Organization (WHO), is a BMI of 30 or higher. This classification includes three categories of obesity: Class I (BMI of 30-34.9), Class II (BMI of 35-39.9), and Class III (BMI of 40 or higher). A BMI of ≥30 is used as the threshold for obesity because it correlates with an increased risk of various health problems, such as diabetes, cardiovascular disease, and certain types of cancer.

## **Why Each Wrong Option is Incorrect**
- **Option A:** A BMI less than 18.5 is classified as underweight. Therefore, this option is incorrect for obesity.
- **Option B:** A BMI between 18.5 and 24.9 is considered normal weight. Hence, this option does not represent obesity.
- **Option D:** While a BMI of 25-29.9 is categorized as overweight, it does not meet the criteria for obesity.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that BMI is not a perfect measure, as it does not directly assess body fat or distinguish between lean body mass and body fat. However, for clinical and population-level assessments, BMI remains a useful and practical tool.

## **Correct Answer:** . ≥30.