Question

Which of the following has the largest number of atoms?

• A. $0.5\text{g}$ atom of $Cu$
• B. ${10}^{23}$ atoms of $Cu$
• C. $0.623\text{g}$ of $Cu$
• D. $3.175\text{g}$ of $Cu$

Answer 1

The correct option is A $0.5\text{g}$ atom of $Cu$

Mass of $Cu=63.5\text{g}$
a. $1\text{gm atom}$ = $1\text{mole}$
$0.5\text{gm atom}$ = $0.5\text{mole}$
$\text{Number of atoms in}1\text{mole}=6.023\times {10}^{23}$
$\text{Number of atoms in}0.5\text{mole}=0.5\times 6.023\times {10}^{23}=3.011\times {10}^{23}$

b. $\text{Number of atoms of}Cu={10}^{23}$

c. $\text{Number of moles}=\frac{\text{given weight}}{\text{molar mass}}=\frac{0.623}{63.5}=0.009811$
$\text{Number of atoms}=\text{no of moles}\times 6.023\times {10}^{23}=5.91\times {10}^{21}$

d. $\text{Number of moles}=\frac{\text{given weight}}{\text{molar mass}}=\frac{3.175}{63.5}=0.05$
$\text{Number of atoms}=\text{no of moles}\times 6.023\times {10}^{23}=3.0\times {10}^{22}$