Question

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there are more hydrogen atoms in living organisms than any other atom, but oxygen is more abundant in terms of mass. why is this statement true?
options:
hydrogen atoms have a lower mass than oxygen atoms.
hydrogen is present as single atoms and oxygen is bonded in compounds.
hydrogen is a gas, but oxygen is a solid.
hydrogen atoms make up more of water’s mass than oxygen atoms.

Explanation:

To determine why there are more hydrogen atoms but oxygen is more abundant by mass in living organisms, we analyze each option:

• Option 1 ("Hydrogen atoms have a lower mass than oxygen atoms"): While hydrogen has lower mass, this alone doesn't explain the abundance by mass.
• Option 2 ("Hydrogen is present as single atoms and oxygen is bonded in compounds"): In living organisms, both H and O are often in compounds (e.g., water, organic molecules), so this is incorrect.
• Option 3 ("Hydrogen is a gas, but oxygen is a solid"): Both H₂ and O₂ are gases under biological conditions, and this doesn't relate to mass abundance in organisms.
• Option 4 ("Hydrogen atoms make up more of water’s mass than oxygen atoms"): In water ($\ce{H_2O}$), the mass of O (16 g/mol) is greater than the combined mass of 2 H (2 g/mol). However, living organisms have a lot of water and organic molecules with H and O. Since H atoms are numerous (e.g., each water has 2 H, 1 O) but O has higher atomic mass, the total mass of O ends up being more. The key is that even though H atoms are more in number, O's higher atomic mass (16 vs. H's 1) means that when considering mass, O contributes more. The correct reasoning ties to the fact that hydrogen atoms are numerous (due to being in many compounds like water, where there are 2 H per O) but oxygen has a much higher atomic mass, so the total mass from O is greater. The option that aligns is the one about hydrogen atoms having lower mass (but more precisely, the combination of number of H atoms and O's higher mass). Wait, re - evaluating: The correct explanation is that hydrogen atoms are present in large numbers (e.g., in water, carbohydrates, etc.) but each hydrogen atom has a very low mass (1 atomic mass unit) compared to oxygen (16 atomic mass units). So even though there are more H atoms, the total mass from O (because of its higher mass per atom and its presence in many compounds) is greater. Among the options, the one stating "Hydrogen atoms have a lower mass than oxygen atoms" is the key part of the explanation. But also, the option "Hydrogen atoms make up more of water’s mass than oxygen atoms" is incorrect (in $\ce{H_2O}$, O is ~89% of mass). Wait, the correct option should be the one that explains that hydrogen has lower atomic mass, so even with more atoms, oxygen (higher mass per atom) contributes more to total mass. So the correct option is "Hydrogen atoms have a lower mass than oxygen atoms" (along with the fact that H is present in many compounds with multiple H per O, but the lower mass of H is the core reason for O being more abundant by mass despite more H atoms).

Answer:

The correct option is: "Hydrogen atoms have a lower mass than oxygen atoms" (assuming this is one of the options, likely the first boxed option in the image - based on the text, the option "Hydrogen atoms have a lower mass than oxygen atoms" is the correct explanation as lower mass of H means that even with more H atoms, the higher mass of O atoms leads to O being more abundant by mass in living organisms due to the combination of atomic mass and the number of atoms (with H being in many compounds but each H having low mass).