"Milliliter" is a unit of capacity, and "gram" is a unit of mass. The two cannot be equated. To know how many grams a substance is in 100 milliliters, you need to know its density (unit: g/ml), and multiply its number of milliliters by its density to get its mass. The density of water is 1g/ml, then 100ml of water is 100mlx1g/ml=100g.

Milliliter is a unit of volume, corresponding to cubic centimeters, and the main unit of volume unit is liter (L). 1L=1000mL, 1000ml=1000 cubic centimeters, 1000ml=1cubic decimeters.

Gram is the unit of mass, symbol g. One gram has the mass of approximately 0.501×10^23 C-12 atoms, which is equivalent to the mass of one cubic centimeter of water at 4 degrees Celsius.