When a fixed amount of ideal gas goes through an adiabatic expansion: a. its internal (thermal) energy does not change.
b. the gas does no work.
c. no heat enters or leaves the gas.
d. its temperature cannot change.
e. its pressure must increase.

C

Explanation:

C - No heat enters or leaves the gas.

Adiabatic Expansion can be defined be saying, it is an expansion in which no heat is added to or no heat is subtracted from the air. This lack of addition or subtraction, cools during the expansion because of the work that would be done by the air. And as such, we can say that No heat enters the gas, and no heat leaves the gas in the same manner.

I hope that's clear enough

b) phosphorus pentoxide

the entire statement is true and correct.  

there's no diagram, nothing is illustrated, and no question is asked.