To solve this problem, we need to analyze each statement about photons.$\\$A. The energy of a photon is $E = h\nu. \\$This statement is correct. The energy of a photon is given by the equation $E = h\nu,$ where $h$ is Planck's constant and $\nu$ is the frequency of the photon.$\\$B. The velocity of a photon is $c. \\$This statement is correct. Photons travel at the speed of light $c$ in free space.$\\$C. The momentum of a photon $p = \frac{h\nu}{c}. \\$This statement is correct. The momentum of a photon is given by $p = \frac{E}{c} = \frac{h\nu}{c}. \\$D. In a photon-electron collision, both total energy and total momentum are conserved.$\\$This statement is correct. In any collision, including photon-electron collisions, both energy and momentum are conserved.$\\$E. Photon possesses positive charge.$\\$This statement is incorrect. Photons are neutral particles and do not have any charge.$\\$Based on the analysis, the correct statements are A, B, C, and D.$\\$Therefore, the correct option is 4: A, B, C, and D only.