Perhaps I'm making this overly complicated, as I tend to do sometimes, but the question asks which element does NOT occur as a distinct allotrope between 0°C and 150°C, and the answer is silicon. However, I just googled it and it says right here: "Two allotropes of silicon exist at room temperature: amorphous and crystalline." http://education.jlab.org/itselemental/ele014.html
Since room temperature is between 0°C and 150°C, and it is highly unlikely that the answer key is wrong, is there something specific about the definition "distinct allotrope" so that amorphous doesn't count or something? Why is the answer silicon?