In a photoelectric effect experiment, the stopping potential is...

According to Einstein's photoelectric equation:

$eV_s = \dfrac{hc}{\lambda} - \phi$

where $V_s$ is the stopping potential, $\lambda$ is the wavelength of incident light, and $\phi$ is the work function of the material.

Using the standard value $hc \approx 1240 \text{ eV nm}$, we can calculate the work function for the given data points.

For $\lambda = 400 \text{ nm}$ and $V_s = 1.00 \text{ V}$:

$\phi = \dfrac{1240}{400} - 1.00$

$\phi = 3.10 - 1.00 = 2.10 \text{ eV}$

For $\lambda = 500 \text{ nm}$ and $V_s = 0.38 \text{ V}$:

$\phi = \dfrac{1240}{500} - 0.38$

$\phi = 2.48 - 0.38 = 2.10 \text{ eV}$

The calculated work function is approximately $2.10 \text{ eV}$. Among the given choices, the closest value is $2.15 \text{ eV}$.

Answer: $2.15 \text{ eV}$