According to Einstein's photoelectric equation, the graph between the kinetic energy of photoelectrons ejected and the frequency of incident radiation is

Photoelectric effect experiments are performed using three different metal plates p, q and r having work functions ${\mathrm{\varphi }}_{\mathrm{p}}=2.0\mathrm{eV},{\mathrm{\varphi }}_{\mathrm{a}}=2.5\mathrm{eV}$ and ${\mathrm{\varphi }}_{\mathrm{r}}=3.0\mathrm{eV}$ respectively, A light beam containing wavelength of $550\mathrm{nm}, 450\mathrm{nm}$ and $350\mathrm{nm}$ with equal intensities illuminates each of the plates. The correct $\mathrm{I}-\mathrm{V}$ graph for the experiment is, see Fig. $19.15$ 

Sodium and copper have work function $2.3 \text{eV}$ and $4.5 \text{eV}$ respectively. Then, the ratio of the wavelength is nearest to: