Step 1: Start with the given equation.
The given equation is:
\[
\left( \frac{p}{q} \right)^q = p^{\left(\frac{p}{q} - 1\right)}.
\]
Rewriting \( \left( \frac{p}{q} \right)^q \):
\[
\left( \frac{p}{q} \right)^q = \frac{p^q}{q^q}.
\]
Thus,
\[
\frac{p^q}{q^q} = p^{\left(\frac{p}{q} - 1\right)}.
\]
Step 2: Analyze the powers of \( p \) and \( q \).
From the equation above, equate the terms involving \( p \) and \( q \):
\[
p^q = q^p.
\]
Step 3: Verifying the result.
The relationship \( p^q = q^p \) satisfies the given equation and matches option (a).