Answer:
Methane
Step-by-step explanation:
The gas that you could keep in an outdoor storage tank in winter in Alaska is Methane.
The reason is the extreme low temperature during the winter. The boiling point of butane is 44 ºF ( -1ºC) and that of propane is a higher -43.6 º F but still within the range of average minimum winter temperature in Alaska (-50 ªF). Therefore we will have condensation in the tanks and not enough gas pressure.
Methane having a boling point of -259 ºF will not condense at the low wintertime temperatures in Alaska.