Answer
a) the period will decrease
b) III
Work Step by Step
(a) As we know that $T=2\pi\sqrt{\frac{l}{g}}$. This equation shows us that the time period of a pendulum is directly proportional to the square root of the length of the pendulum. At low temperature we will have thermal contraction. Thus, the length of the pendulum decreases and as a result its time period also decreases.
(b) The correct option is statement (III) -- that is, cooling shortens the aluminum rod, which decreases the period of the pendulum.
