Answer
$$\frac{T_{2}}{T_{1}} =\frac{1}{2}$$
Work Step by Step
From ideal gas law $$\frac{P_{1}V_{1}}{T_{1}}=\frac{P_{2}V_{2}}{T_{2}}$$ Here we have $P_{1} = 4$ $V_{1}=1$ $P_{2}=1$ $V_{2}= 2$
$$\therefore\frac{T_{2}}{T_{1}}=\frac{P_{2}V_{2}}{P_{1}V_{1}}=\frac{1\times2}{4\times1}=\frac{1}{2}$$
