Step 1: Concept
In thermodynamics, the work done during a reversible transformation is calculated by integrating the expression $W = -\int P \, dV$.
Step 2: Meaning
For an ideal gas equation, we substitute $P = \frac{nRT}{V}$ into the integral since the process is isothermal ($T$ remains constant).
Step 3: Analysis
Performing the definite integration from the initial volume $V_{1}$ to the final volume $V_{2}$:
$$W = -\int_{V_{1}}^{V_{2}} \frac{nRT}{V} \, dV = -nRT \int_{V_{1}}^{V_{2}} \frac{1}{V} \, dV$$
$$W = -nRT [\ln V]_{V_{1}}^{V_{2}} = -nRT \ln\left(\frac{V_{2}}{V_{1}}\right)$$
Step 4: Conclusion
This matches the standard thermodynamic representation for reversible isothermal work done by an expanding system.
Final Answer: (A)