In an average adult human, the weight of the brain is approximately what percentage of the total body weight?

Introduction / Context:
The human brain is a highly important organ, controlling thoughts, movements, and many automatic functions. Although it is crucial, it is not very large compared to the entire body. Many general knowledge and biology questions ask what percentage of body weight the brain represents in an average adult. Knowing this helps illustrate how a relatively small organ can consume a significant amount of energy and perform complex functions.

Given Data / Assumptions:

• We are considering an average healthy adult human.
• The brain typically weighs around 1.2 to 1.5 kilograms.
• An average adult body weight is assumed to be about 60 to 70 kilograms.
• The options range from 2 percent to 5 percent of body weight.

Concept / Approach:
If we take a typical brain weight of about 1.3 kilograms and a body weight of about 65 kilograms, we can estimate the percentage. Dividing 1.3 by 65 gives approximately 0.02, which corresponds to 2 percent. This simple calculation shows that the brain is about 2 percent of the total body weight in an average adult. Even though this percentage is small, the brain uses a disproportionately large share of the body's energy, reflecting its high activity level. Therefore, the option stating about 2 percent is the correct one.

Step-by-Step Solution:
Step 1: Assume an average adult body weight of about 60 to 70 kilograms. Step 2: Recall that the average adult human brain weighs roughly 1.2 to 1.5 kilograms; a commonly used figure is around 1.3 kilograms. Step 3: Estimate the ratio of brain weight to body weight. For example, 1.3 divided by 65 is approximately 0.02. Step 4: Convert this decimal to a percentage by multiplying by 100, which yields 2 percent. Step 5: Compare this result with the answer choices and select the option that states about 2 percent of body weight.

Verification / Alternative check:
Many biology and medical references specify that the human brain accounts for about 2 percent of body weight but uses about 20 percent of the body's oxygen and energy at rest. This contrast is often highlighted to show how metabolically active the brain is. Educational materials and exam keys consistently use the figure of approximately 2 percent rather than higher percentages. This repeated use of the 2 percent estimate confirms that it is the accepted approximate value for GK purposes.

Why Other Options Are Wrong:
About 3 percent, 4 percent, or 5 percent of body weight are all overestimates when compared to typical brain and body weight figures. If the brain were 3 percent of body weight, a 60 kilogram person would have a brain weight of about 1.8 kilograms, which is significantly higher than the usual range. Higher percentages exaggerate the relative size of the brain in the body and do not match standard physiological data.

Common Pitfalls:
Some students assume that because the brain is so important, it must be large in proportion to the body and choose a higher percentage. Others may remember that the brain consumes about 20 percent of the body's energy and confuse this number with its share of body weight. To avoid these mistakes, keep two separate facts in mind: the brain is about 2 percent of body weight but uses about 20 percent of resting energy. This clear separation helps you choose the correct percentage for weight without confusion.

Final Answer:
The correct option is About 2 percent of body weight, which is the approximate share of total body weight taken up by the human brain in an average adult.