AIIMS 2019 Physics Work Function MCQ Question

The work function (ϕ) of a material is inversely proportional to its threshold wavelength (λ), expressed as ϕ ∝ 1/λ. For sodium (Na) and copper (Cu), the threshold wavelengths are approximately 589 nm and 300 nm, respectively. Calculating the ratio of their threshold wavelengths gives λ_Na/λ_Cu = 589 nm / 300 nm ≈ 1.96, which rounds to 2, indicating that sodium has a longer threshold wavelength than copper. However, since the question asks for the ratio of the work functions, which is inversely related to the threshold wavelengths, the ratio of work functions is approximately 3, making option C correct. Other options are incorrect as they do not accurately reflect the relationship between work function and threshold wavelength for these two metals.