Concept:
The coefficient of volume expansion is defined as
\[
\alpha
=
\frac{1}{V}
\left(\frac{\partial V}{\partial T}\right).
\]
For an ideal gas,
\[
PV=nRT.
\]
Step 1: Use the given condition.
Given,
\[
P^2T=\text{constant}.
\]
Therefore,
\[
P^2=\frac{k}{T},
\]
where \(k\) is a constant.
Hence,
\[
P=\frac{\sqrt{k}}{\sqrt{T}}
\propto T^{-1/2}.
\]
Step 2: Express volume in terms of temperature.
Using the ideal gas equation,
\[
V=\frac{nRT}{P}.
\]
Since
\[
P\propto T^{-1/2},
\]
we get
\[
V\propto T\times T^{1/2}.
\]
\[
V\propto T^{3/2}.
\]
Let
\[
V=C\,T^{3/2},
\]
where \(C\) is a constant.
Step 3: Differentiate with respect to temperature.
\[
\frac{dV}{dT}
=
\frac{3}{2}CT^{1/2}.
\]
Therefore,
\[
\alpha
=
\frac{1}{CT^{3/2}}
\left(\frac{3}{2}CT^{1/2}\right).
\]
\[
\alpha
=
\frac{3}{2T}.
\]
Step 4: Write the final answer.
\[
\boxed{\alpha=\frac{3}{2T}}
\]
\[
\boxed{\text{Answer = (D)}}
\]