The correct option is **B. 4.00 grams**. ### Detailed Explanation: 1. **Understanding Avogadro's Number**: - Avogadro's number, \( N_A \), is defined as \( 6.022 \times 10^{23} \) particles (atoms, molecules, etc.) per mole. This means that one mole of any substance contains \( 6.022 \times 10^{23} \) of its constituent particles. 2. **Molar Mass of Helium**: - The molar mass of helium (He) is approximately 4.00 grams per mole. This value indicates that one mole of helium atoms (which is \( 6.022 \times 10^{23} \) helium atoms) has a mass of 4.00 grams. 3. **Calculating the Mass of One Avogadro Number of Helium Atoms**: - Since one mole of helium atoms corresponds to Avogadro's number, the mass of one Avogadro number of helium atoms is simply the molar mass of helium: \[ \text{Mass of 1 mole of He} = 4.00 \text{ grams} \] - Therefore, the mass of one Avogadro number of helium atoms is **4.00 grams**. ### Why Other Options Are Incorrect: - **Option A: 1.00 gram**: - This option is incorrect because it does not correspond to the molar mass of helium. Helium is a light element, but its molar mass is significantly higher than 1.00 gram per mole. - **Option C: 8.00 grams**: - This option is also incorrect. While it might seem plausible if one were to mistakenly think of two moles of helium (since 2 moles would indeed weigh 8.00 grams), the question specifically asks for the mass of one Avogadro number (one mole) of helium atoms. - **Option D: 6.00 grams**: - This option is incorrect as well. There is no basis for this value in the context of helium's molar mass. It does not correspond to any standard measurement of helium. ### Common Pitfalls: - **Confusing Moles with Mass**: Students often confuse the number of moles with the mass. Remember that the molar mass is the mass of one mole of a substance. - **Misunderstanding Avogadro's Number**: It's crucial to remember that Avogadro's number refers to the number of particles in one mole, not the mass. - **Rounding Errors**: When dealing with molar masses, ensure you use the correct significant figures based on the context of the problem. ### Revision Summary: - Avogadro's number is \( 6.022 \times 10^{23} \) particles per mole. - The molar mass of helium is approximately 4.00 grams per mole. - The mass of one Avogadro number of helium atoms is 4.00 grams. - Always differentiate between moles and mass to avoid confusion in calculations.