So if I frozen 50 ML of water, it turns into ice cube. Would the ice cube weigh the same as the 50 ML of water it was before?
Yes, as the amount, i.e. the number of molecules involved, does not change. Unless you look at it from a relativistic point of view, where you have to subtract the mass equivalent of the heat that is taken out of the water by cooling it down and freezing it and possibly cooling it further.