The molar mass of Cadmium is 112.41 grams, so first you need to convert your given value to moles. To do that divide 3 grams by the molar mass of 112.41 grams. That gives you an answer of .0267 moles of cadmium. Then to convert that value to atoms, you must use the constant of 6.022X10^23 atoms in one mole. Multiply the moles by that number, which will give you a final answer of (1.61X10^22) atoms in 3 grams of cadmium.
Hope this helps!
