$1$ mole of atoms is equal to: 

The number of moles in $15.6$ g of potassium is:     

$\left[\mathrm{K}=39\right]$

The number of moles in $28.4$ g of chlorine atoms ($\mathrm{CI}$) is: 

$\left[\mathrm{Cl}=35.3\right]$

The number of moles in $100 \mathrm{g}$ argon is:

$\left[\mathrm{Ar}=40\right]$

The mass of $0.25$ moles of silver is: 

$\left[\mathrm{Ag}=108\right]$

The number of atoms in 0.05 g of hydrogen is: 

$\left[\mathrm{H}=1\right]$