**Core Concept**
The Body Mass Index (BMI) is a widely used measure to categorize individuals into various weight status categories, including underweight, normal weight, overweight, and obese. BMI is calculated using the individual's weight in kilograms and height in meters. This ratio provides a simple and effective way to assess body fat and its associated health risks.

**Why the Correct Answer is Right**
BMI is calculated by dividing the individual's weight in kilograms by the square of their height in meters. This calculation yields a value that is dimensionally consistent with the units of mass (kilograms) and area (square meters). The formula is BMI = weight (in kg) / height² (in meters). By using kilograms and meters, the resulting ratio has the correct units of mass per area, which is essential for accurate BMI calculations. Kilogram/meter² is the correct unit for BMI, as it accurately reflects the ratio of body mass to body surface area.

**Why Each Wrong Option is Incorrect**
**Option A:** Gram/metre² - This option is incorrect because BMI is typically calculated using kilograms, not grams, as the unit of mass. Grams are too small a unit for accurate BMI calculations.
**Option B:** Gram/centimetre² - This option is incorrect because BMI calculations involve meters, not centimeters, as the unit of length. Additionally, grams are again too small a unit for accurate BMI calculations.
**Option D:** Kilogram/centimetre² - This option is incorrect because BMI calculations involve meters, not centimeters, as the unit of length.

**Clinical Pearl / High-Yield Fact**
When calculating BMI, remember that the formula is weight (in kg) / height² (in meters). This formula provides an accurate and consistent measure of body mass relative to body surface area, making it a valuable tool for assessing weight status and associated health risks.

**✓ Correct Answer: C. Kilogram/ metre²**