The photoelectric effect is the phenomenon where electrons are emitted from a material when it is exposed to light or other electromagnetic radiation. The photoelectric equation, Kmax = hv φ0, relates the maximum kinetic energy of the emitted electrons (Kmax) to the frequency of the incident light (v) and the work function of the material (φ0).

I. Kmax is negative:
If Kmax is negative, it implies that the kinetic energy of the emitted electrons is in the opposite direction of the incident light. This is not possible because the electrons should gain energy from the incident light and move in the same direction. Therefore, photoelectric emission will not be possible if Kmax is negative.

II. Kmax is positive:
If Kmax is positive, it means that the kinetic energy of the emitted electrons is in the same direction as the incident light. This is the expected outcome in the photoelectric effect, as the electrons absorb energy from the incident light and gain kinetic energy. Therefore, photoelectric emission is possible if Kmax is positive.

III. v:
The frequency of the incident light, v, plays a crucial role in determining whether photoelectric emission is possible. According to the photoelectric equation, the maximum kinetic energy of the emitted electrons is directly proportional to the frequency of the incident light. If the frequency of the incident light is below a certain threshold, called the threshold frequency, then no electrons will be emitted regardless of the intensity of the light. This is because the energy of the incident light is not sufficient to overcome the work function of the material, φ0. Therefore, photoelectric emission is only possible if the frequency of the incident light is equal to or greater than the threshold frequency.

In summary, photoelectric emission will not be possible if Kmax is negative or if the frequency of the incident light is below the threshold frequency. Photoelectric emission is only possible when Kmax is positive and the frequency of the incident light is equal to or greater than the threshold frequency.