Final answer:
The equivalent capacitance of two capacitors in parallel, which are 2.0 mF and 4.0 mF, is 6.0 mF, making the correct answer B) 6.0 mF.
Step-by-step explanation:
When two capacitors are used in parallel in a circuit, their capacitances add up to give the total capacitance of the combination. This is because the potential difference across each capacitor in parallel is the same, which allows the charges to add up. Therefore, for two capacitors with capacitances of 2.0 mF and 4.0 mF in parallel, the equivalent single capacitor would have a capacitance that is the sum of the two:
Ctotal = C1 + C2 = 2.0 mF + 4.0 mF = 6.0 mF.
Thus, the correct answer to the student's question is B) 6.0 mF.