Molarity =number of mole solute/volume (L) solution.
volume (L) solution = 2.50 L
Molarity= 0.100 M KCl
0.100 M KCl =number of mole solute/2.50 L solution
number of mole solute(KCl)= 0.100 M KCl*2.50 L =0.100*2.50 (mol/L)*L =
=0.250 mol KCl
mass (solute) KCl = Molar mass KCl* number of mole solute(KCl)
Molar mass KCl = 39.1+35.5= 74.6 g/mol
0.250 mol KCl * 74.6 g/mol KCl = 18.7 g KCl