Question

How many atoms in 12.5 grams of sodium?

Answer 1

mol of Na =
`(Mass of Na)/(Molar Mass of Na)`

=
`(12.5g)/(23.00g/mol)`

= 0.54 mol

# atoms of Na = mol × avogadro's constant

= 0.54 mol × [6.02 × 10²³]

= 3.25 × 10²³

Answer 2

22.99 mol in one gram of sodium, so: 12.5/22.99=0.543714659 mol.
Round it to whatever you need to.