The correct answer is: Oxygen.
Oxygen is the most abundant element in the human body, making up about 65% of our body weight. It is found in water, which makes up about 60% of our body weight, and in the proteins, carbohydrates, and fats that make up our cells. Oxygen is essential for life, as it is used in cellular respiration to produce energy.
Carbon is the second most abundant element in the human body, making up about 18% of our body weight. It is found in all organic compounds, including proteins, carbohydrates, and fats. Carbon is also found in the bones and teeth.
Hydrogen is the third most abundant element in the human body, making up about 10% of our body weight. It is found in water and in organic compounds. Hydrogen is also found in the bones and teeth.
Nitrogen is the fourth most abundant element in the human body, making up about 3% of our body weight. It is found in proteins and nucleic acids. Nitrogen is also found in the bones and teeth.
The remaining 4% of the human body is made up of a variety of other elements, including calcium, phosphorus, potassium, sulfur, sodium, chlorine, magnesium, iron, zinc, iodine, selenium, copper, fluorine, chromium, manganese, molybdenum, and cobalt. These elements are essential for life, as they are found in all living things.