1.50*10^23 molecules/ (6.02*10^23 molecules/mol)= 0.249 mol.
There is 0.249 mol in 1.50*10^23 molecules~
The answer is 0.0035
In order to figure out kg, you have to know that 1 milligram is equal to 1/100000 kilograms. You take the amount of mg's that you have, which is 3500, and divide it by 1000000 which will give you your answer.
3500/1000000= 0.0035 kg