A

Statement I: Photocurrent does not linearly increase with frequency of incident light. The photocurrent depends primarily on the intensity of the incident light and not its frequency. The frequency must be above the threshold frequency for electrons to be emitted, but once that frequency is reached, increasing the frequency further does not increase current.
Statement II: This statement is correct. The minimum wavelength of incident radiation below which no photoelectric emission takes place is indeed called the threshold wavelength.
Statement III: This statement is also correct. The minimum negative potential for which the photocurrent stops is referred to as the stopping potential.

Since statements II and III are correct and statement I is incorrect, the correct option is A: Both II and III.