Photoelectric Effect: Einstein's Equation question from JEE Main 2025 (3 Apr, Shift 1)

Answer: (c)

1. Threshold $\lambda_0 = \dfrac{1240\text{ eV nm}}{3\text{ eV}} \approx 413\text{ nm}$
2. Light must have $\lambda \le 413\text{ nm}$, i.e. the short-wavelength (blue–violet) end of the visible spectrum.
3. Red, yellow and green (above $490\text{ nm}$) cannot work; blue is the shortest-wavelength option.
4. So the answer is (c) Blue.