Question

What will be the mass of one ${}^{12}C$ atom in g ?

Answer 1

The molar mass of C-12 is 12 g/mol.
1 mole of C-12 contains avogadro's number of atoms.
Thus, the mass of 1 C-12 atom will be $\frac{12}{6.023\times {10}^{23}}=1.9927\times {10}^{-23}g$.