A small lead block has a mass of 6.8 g. How many atoms of lead (Pb) are present in the block? (Atomic mass of Pb = 207 g/mol, Avogadro's number = 6.022 × 10^{23} mol^{-1})

• A. 2.36 × 10^{23} atoms
• B. 4.12 × 10^{21} atoms
• C. 6.02 × 10^{24} atoms
• D. 1.98 × 10^{22} atoms

Answer: (D)

Verified step by step guidance

1. Convert the mass of the lead block from grams to moles using the atomic mass of lead. Use the formula: \(\text{moles of Pb} = \frac{\text{mass of Pb (g)}}{\text{atomic mass of Pb (g/mol)}}\).
2. Substitute the given values into the formula: mass = 6.8 g and atomic mass = 207 g/mol to find the number of moles of lead in the block.
3. Use Avogadro's number to convert moles of lead to number of atoms. The formula is: \(\text{number of atoms} = \text{moles of Pb} \times 6.022 \times 10^{23} \text{ atoms/mol}\).
4. Multiply the moles of lead calculated in step 2 by Avogadro's number to find the total number of lead atoms in the block.
5. Express the final answer in scientific notation to match the format of the given options.