The answer for this question is 35 gram
The molar mass of KOH is 56 gram
250mL = 0.25 L
The molarity of the solution is = 2.5M
mass = molarity (in gram) x molar mass x volume (in Liter)
Now we just need to insert the number above into the formula
mass = 2.5 x 56 x 0.25
mass = 35 gram