The above answer in this case is incorrect as volumes are provided so n = m/MM cannot be used as this is utilised when masses are provided. In this case there is a gas law which you have to remember. Which is Avogadros Law: it states under the same temperature and pressure, equal volumes of different gases contain the same number of molecules (and thereby the same number of moles).
So basically it's saying you can just do molar ratios with the volumes. In this case there is no limiting reagent as the 3:1 ratio is maintained with 75mL F2: 25 mL Cl2.
Therefore, just compare one of the volumes like you would with molar ratios. For example, we could say n(ClF3) = 2n(Cl2)
Replace moles with volumes because of the Avogadros Law being correct, so v(ClF3) = 2v(Cl2)
v(ClF3) = 2(25) = 50 mL