How many atoms are in 121 g of calcium?
Atomic mass Ca = 40.078 u.m.a40.078 g --------------- 6.02x10²³ atoms121 g ------------------- ??121 x ( 6.02x10²³) / 40.078 =7.28x10²⁵ / 40.078 = 1.81x10²⁴ atoms