In terms of mass percentage, which sequence correctly represents the major elemental composition of an average adult human body?

Introduction / Context:
The human body is made up mainly of a few key elements, and understanding their relative proportions is important in biology and biochemistry. While there are many trace elements, four major elements dominate body mass: oxygen, carbon, hydrogen, and nitrogen. This question asks you to identify the correct order of these elements by mass percentage in an average adult human body.

Given Data / Assumptions:

• The elements considered are oxygen (O), carbon (C), hydrogen (H), and nitrogen (N).
• The options provide different possible sequences of these four elements in decreasing order of mass percentage.
• We assume an average healthy adult with typical body composition, acknowledging that exact percentages can vary slightly among individuals.

Concept / Approach:
Approximate mass percentages of the major elements in the human body are often given as: oxygen about 60 to 65 percent, carbon about 18 percent, hydrogen about 9 to 10 percent, and nitrogen about 3 percent. From these values, it is clear that oxygen is the most abundant element by mass, largely because water makes up a large fraction of body weight and water contains oxygen. Carbon is second because it forms the backbone of organic molecules such as proteins, carbohydrates, and lipids. Hydrogen is third, present in both water and organic compounds, and nitrogen is fourth, mainly found in amino acids and nucleic acids. Therefore, the correct descending order by mass is O > C > H > N.

Step-by-Step Solution:

Verification / Alternative check:
Biology texts that discuss chemical composition of the human body typically present tables or charts showing element percentages. These consistently show oxygen as the most abundant element by mass, followed by carbon, then hydrogen, and finally nitrogen among the four major elements. While specific percentages vary slightly depending on the source, the order remains the same. This robust agreement across references confirms that O > C > H > N is the correct sequence by mass percentage for an average adult human body.

Why Other Options Are Wrong:

C > O > H > N is wrong because it places carbon above oxygen; in reality, oxygen is more abundant due to the high water content of the body.

O > H > C > N is incorrect because it places hydrogen above carbon; although hydrogen atoms are numerous, their low mass means that the total mass of hydrogen is less than that of carbon.

N > C > O > H is clearly wrong because nitrogen is the least abundant of the four by mass, not the most abundant.

Common Pitfalls:
Students sometimes think that carbon must be the most abundant because life is called carbon based. Another pitfall is to focus on the number of atoms rather than their mass; hydrogen has many atoms but each atom is very light. To avoid these mistakes, remember that water dominates body mass and water contains a lot of oxygen, making oxygen come first. Thus, the correct descending order of major elements by mass in an average adult human body is O > C > H > N.

Final Answer:
Therefore, the correct sequence for the major elemental composition of the adult human body by mass is O > C > H > N.