How many grams of K2Cr207 are in 250. mL of 0.500M of K2Cr207: 36.8 g
73.6 g
294 g
18.2 g

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

"record the time to complete a chemical reaction" would most likely be part of a lab procedure.