What kind of pad does the Quartus select when I configure the i/o as single-ended .

To configure a pin as single-ended, you simply set the I/O standard for that pin to one of the supported single-ended I/O standard. This can be done using the Assignment Editor or the Pin Planner. If you want to use a differential standard, you do the same thing only choose a supported differential I/O standard and make the assignment only to the positive pin in the pair. The negative pin will automatically take on the required assignment. In your design, don't include the negative pin and just treat the positive pin as if it were single-ended.