The human brain uses about 20% of the total oxygen and blood in the body. Even though the brain is only about 2% of the body’s weight, it requires a very large amount of energy to function properly.

This high demand for oxygen and blood is because the brain is always active. Whether you are awake or asleep, your brain is constantly working. It controls your heartbeat, breathing, thinking, movement, memory, and all body functions.

Oxygen is carried to the brain through the blood. Without enough oxygen, brain cells can become damaged in just a few minutes. That is why it is very important for the brain to have a steady supply of oxygen-rich blood.

Let’s look at the options:
- 12% and 35% are too low for the brain’s needs.
- 48% is too high and not supported by scientific facts.
- The correct answer is 20% — this is what most scientists and doctors agree upon.

This also shows why problems like stroke (when blood flow to the brain is blocked) are very dangerous. Even a short break in oxygen can cause brain damage.

In summary, the brain needs a lot of oxygen and blood to do its job, even though it is small. That’s why it uses 20% of your body’s total supply.