Einstein's photoelectric equation is given by

$$K_{\max} = h\nu - \phi,$$

where $K_{\max}$ is the maximum kinetic energy of the emitted photoelectrons, $h$ is Planck's constant, $\nu$ is the frequency of the incident radiation, and $\phi$ is the work function of the metal (the minimum energy needed to eject an electron).

If you plot $K_{\max}$ against $\nu$, you will get a straight line with slope $h$ (Planck's constant) and y-intercept $-\phi$ (the negative of the work function). The slope of the line (which is $h$) does not depend on the intensity of the radiation or the type of metal used. Instead, it is a universal constant.

Therefore, the correct answer is:

Option D: The slope is the same for all metals and independent of the intensity of the radiation.