Note that the carbon is #12# which is already known in the question..
But first, recall that;
#"no of moles of carbon" = ("no of entity" ("atoms"))/"avogadros constant"#
Where;
#"no of moles of carbon" = "mass"/"molar mass"#
#"avogadros constant" = 6.022 × 10^23#, representing the number of atoms..
#"no of entity" = "number of carbon atoms present"#
First, we have to know the no of moles of carbon, and to get that, we should use;
#"no of moles of carbon" = "mass"/"molar mass"#
Where;
#"mass" = 0.012g#
#"molar mass" = 12gmol^-1#
Substituting the values we should have;
#"no of moles of carbon" = (0.012cancelg)/(12cancelgmol^-1) = 0.001mol#
Now, having;
#"no of moles of carbon" = ("no of entity" ("atoms"))/"avogadros constant"#
#"no of entity" ("atoms") = "no of moles of carbon" xx "avogadros constant"#
#"no of entity" ("atoms") = 1 xx 10^-3 xx 6.022 × 10^23#
#"no of entity" ("atoms") = 6.022 × 10^(23 - 3)#
#"no of entity" ("atoms") = 6.022 × 10^20"atoms"#
Hope this helps!