5. 19 Each of the following processes caused the gas volume to double, as shown. For each process, tell how the remaining gas variable
changed or state that it remained fixed:
(a) T doubles at fixed P.
(b) T and n are fixed.
(c) At fixed T, the reaction is $CD_2 (g) \rightarrow C (g) + D_2 (g)$.
(d) At fixed P, the reaction is $A_2 (g) + B_2 (g) \rightarrow 2AB (g)$