e) None of the above
100% N1 is just a number, it doesn't represent any limit or any specific value - I'm sure you can find more about this on the flight testing thread. Maximum N1/N2 values are usually determined by bearing loading - e.g. how fast can the shafts turn without overheating/destroying the bearings.
However, the takeoff/go-around/full rated thrust N1 setting depends strongly on outside air temperature. If we simplify by saying that the engine thrust is linearly corelated with fuel flow and the fuel-to-air ratio remains constant, we can say that the more air you get into the engine, the more thrust the engine will give you. With high temperatures (let's say 35°C), the air density is low and the
volume airflow (and thus N1) has to be increased to maintain the same
mass airflow as we have for example if the temperature is -40°C.
For example, the CFM56-3C1 installed on B737 Classic aircraft is flat-rated at 32°C (so the maximum thrust is constant from 32°C downwards). In order to achieve full rated (takeoff) thrust the N1 at 30°C is 96%, while at -40°C the takeoff N1 is only 84%.