Task: Question Answering
Input (English): Question: Could a glass electrode be used as a reference electrode ?: 
 Options:  <1> Yes, if the glass electrode is a combined electrode. <2> Yes, if a mercury electrode is used as the indicator electrode. <3> No, since the glass electrode is a selective electrode. <4> No, because its foundation is not Nerstian. <5> Yes, if the determination is made in a buffered medium.
Output (English): 5