Molar mass Sodium Fluoride :
NaF = 22.98 + 18.99 => 41.97 g/mol
number of moles ( n ) :
mass of solute / molar mass
2.25 / 41.97 => 0.053 moles
Volume = 25.0 mL in liters : 25.0 / 1000 => 0.025 L
M = n / V
M = 0.053 / 0.025
M = 2.12 mol/L
hope this helps!
