How many ml are in 450g?
None.
A gram is a measure of mass. A millilitre is a measure of
volume. The two measure different things and, according to basic
principles of dimensional analysis, conversion from one to the
other is not valid.
If you are not convinced, consider a millilitre of air. How many
grams? Next consider a millilitre of water. How many grams?
The masses of equal volumes of the two substances will clearly
be very different. So there is no direct conversion between mass
and volume: you need to know the density of the substance to enable
you to carry out the conversion.
Some people still believe that there is a conversion in relation
to pure water but that is only approximately true. Until 1964
(nearly 50 year ago!) a litre was defined as the volume of one
kilogram of pure water at 4 degrees Celsius and at a pressure of
760 millimetres of mercury. With that definition a conversion would
have been possible - but only for pure water and only under those
conditions. That definition of a litre was abandoned in favour of 1
litre =1000 cubic centimetres. So now, even for water, there is no
simple conversion.
In fact the density of pure water at a pressure of 1 bar,
reaches its maximum value at 4 deg C and that value is 0.999 972 0
g/ml.