Step 1: Understanding the Concept:
An electron accelerated through \(V\) has \(\lambda = \frac{h}{\sqrt{2meV}}\), so \(\lambda\propto V^{-1/2}\).
Step 2: Compare:
\(\frac{\lambda_2}{\lambda_1} = \sqrt{\frac{V_1}{V_2}} = 2\), so \(\frac{V_1}{V_2} = 4\).
Step 3: Check:
Doubling the wavelength means quartering the voltage, which fits \(V_1:V_2 = 4:1\).
Final Answer:
The ratio \(V_1:V_2\) is \(4:1\), option (D).
\[ \boxed{4:1} \]