Answer
a. decreases
b. best: I
Work Step by Step
The equation of the state for an ideal gas is$ \quad PV=NkT \quad (17-2)$
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a.
Treat the helium as an ideal gas.
Placing the balloon in the refrigerator, the P and N remain the same, so $\displaystyle \frac{\mathrm{V}_{\mathrm{i}}}{\mathrm{V}_{\mathrm{f}}}=\frac{\mathrm{T}_{\mathrm{i}}}{\mathrm{T}_{\mathrm{f}}}.$
Since the temperature drops, the volume decreases.
b.
I is correct.
II does not take temperature into account.
III is wrong.
