2.45M Potassium Chloride (KCl) means we have 2.45 moles of KCl in 1L of solution.
Amount of moles in 2L of 2.45M KCl `= 2.45xx2 = 4.9 `
Molar mass of KCl = 74.55g/mol
mass = molar mass*moles
Mass of 2L of 2.45M KCl `= 4.9xx74.55g = 365.295g`
So we need 365.295g of KCl to produce the 2.45M KCl solution.
We need to get an accurate scale that can read to 1mg accuracy and measure 365.295g of KCl solid and dissolve it in 2L of water to get the required 2.45M solution.
But that would not produce a 2L solution.
The procedure that is followed in the laboratories is to take the exact mass of the salt first (here, 365.3 g KCl), in a 2 L volumetric flask, add about 1L distilled water, dissolve the salt completely and then fill the volume with distilled water upto the 2 L mark and finally homogenize the solution by thorough mixing.