ml stands for milliliter and that's a volume unit... Perhaps you mean mol?
In that case, 1 mol is a number of particles which equals Avagadro's constant, approx 6.0221415 × 10^23. The mass of a proton is 1.6726231 x 10^-27 kg.
If you do mean milliliter, and if we are talking about the fanciful notion of "if you could pack protons into a milliliter so that they "fill it up" and are all side by side...
Start with the size of the proton which is on at the order of a femptometer (10^-15 m). Since a mililiter is the same as a cubic centimeter, you could say a proton is 10^-13 cm across, therefore 10^13 protons lined up in a row would be 1 cm long.
Cube this number, and you have the number of protons that "fill up" a milliliter: 10^39 protons. Where did that electrostatic force go anyway?
So if each proton has a mass of 1.7 x 10^-27 kg, then the milliliter "full" of protons would have a mass of 1.7 x 10^12 kg. That's about two trillion kilograms.
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