Final answer:
It requires 3 photons to break a nitrogen-nitrogen single bond.
Step-by-step explanation:
Breaking a bond requires energy, which can be supplied in the form of photons. The energy required to break a bond depends on the bond strength. A nitrogen-nitrogen single bond is relatively strong and typically requires multiple photons to break.
In the case of a nitrogen-nitrogen single bond, it would require 3 photons to break the bond. This is because each nitrogen atom in the bond needs to receive an electron to achieve an octet of electrons, and each photon provides one electron.
Therefore, the answer to the question is 3) 3.