given that 1.5 mL of 1.45mM concentration protein received.

Let us convert this into number of millimoles as follows.

1.5 mL of 1.45 mM protein = 1.5 mL x 1.45 millimole / 1000 mL

                                       = 1.5 x 1.45/1000 millimole

                                       = 0.002175 millimole

       given that the protein has the molar mass 12.5 kDa

                                                                = 12500 Da

                                                                = 12500 g / mol

                                                               = 12500 mg / mmol

Therefore 0.002175 mmole protein has the mass = 0.002175 mmol x 12500 mg/mmol

                                                                  = 27.1875 mg

                                                                  = 27.2 mg

Hence the option (B) is the Answer.