MCQ Detailed View

The human body is made up of many chemical elements, but only a few account for most of our total body mass. Understanding the percentage of these elements is an important part of biology because it explains how life depends on basic chemistry.

The most abundant element in the human body is oxygen, which makes up about 65% of body weight. This is because the body is composed of around two-thirds water, and each water molecule contains oxygen. Oxygen is also critical for cellular respiration, the process that allows cells to release energy from food.

The second most abundant element is carbon, which contributes about 18% of the body’s mass. Carbon is the foundation of all organic molecules. It is present in proteins, carbohydrates, lipids, and nucleic acids such as DNA and RNA. Its ability to form four stable bonds with other atoms allows it to create complex structures, which are essential for the chemistry of life. Without carbon, the body could not form the structural and functional molecules that support growth, repair, and energy storage.

The third most abundant element is hydrogen, at around 10%. Hydrogen is part of water and nearly every organic molecule in the body. It plays an essential role in maintaining pH balance, storing energy, and driving metabolic reactions.

Calcium is also a very important element in the human body but represents only about 1.5–2% of body mass, mostly stored in bones and teeth. It helps in muscle contraction, blood clotting, and nerve signaling, but it does not rank among the top three by percentage.

To summarize:

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  Oxygen – ~65%

  
  


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  Carbon – ~18%

  
  


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  Hydrogen – ~10%

  
  

Thus, the correct answer is Carbon (18%), as it is the second most abundant element in the human body.