Step 1: Using the double-slit diffraction formula.
The formula for the distance between adjacent maxima in a double-slit experiment is:
\[
y = \frac{\lambda L}{d}
\]
where:
- \( y \) is the distance between adjacent maxima,
- \( L \) is the distance from the slits to the screen,
- \( d \) is the distance between the slits, and
- \( \lambda \) is the wavelength of the light.
Step 2: Applying the given values.
Given that \( y = 1.2 \, \text{cm} = 0.012 \, \text{m} \), \( L = 1.8 \, \text{m} \), and \( d = 0.54 \, \text{mm} = 0.54 \times 10^{-3} \, \text{m} \), we can rearrange the formula to solve for \( \lambda \):
\[
\lambda = \frac{y d}{L} = \frac{0.012 \times 0.54 \times 10^{-3}}{1.8} \approx 600 \, \text{nm}
\]
Step 3: Conclusion.
The wavelength of the light is 600 nm, so the correct answer is (C).