Analysing the Question:
We are given a 250 mL solution of 0.5M K₂Cr₂O₇
Which means that we have:
0.5 Mole in 1L of the solution
0.125 moles in 250 mL of the solution [dividing both the numbers by 4]
Mass of K₂Cr₂O₇ in the given solution:
Molar mass of K₂Cr₂O₇(Potassium Dichromate) = 194 g/mol
we know that we have 0.125 moles in the 250 mL solution provided
Mass = Number of moles * Molar mass
Mass = 0.125 * 194
Mass = 36.75 grams