How many oxygen atoms in 2.15 mol of N2O?

firstly, you cannot have 1.20105 molecules, it is physically impossible to have a non-integer number of molecules. But I will assume you mean 1.20105 mol.

Simply multiply the number of mols of oxygen atoms by avagadros number

so 1.20105 mol of n205 = 1.20105*5mol of oxygen atoms.

1.20105 x 5 x 6.022e-23 is your answer