This will depend on the substance you are talking about. One mole is by definition equal to 6.02 x 1023 molecules or atoms of the substance, but the weight of one molecule or atom will vary depending...
It depends on the element you are using but you can find mass on the periodic table.
it depends on what element you are talking about
Its avogadros number which is 6.02 X 10^23 g/mol
1 mole C= 12.01 g 4 moles H= 4.04 g Therefore, 1 mole of CH4 = 12.01g + 4.04g = 16.05g