Final answer:
The reaction that represents the first ionization of phosphorus (P) is a) P(g)→P+(g)+e−, where a gaseous neutral phosphorus atom loses one electron to form a positively charged ion.
Step-by-step explanation:
The answer to the question which reaction represents the first ionization of phosphorus (P) is: a) P(g)→P+(g)+e−. The first ionization refers to the process of removing one electron from a gaseous neutral atom to form a cation with a +1 charge. During this process, energy, known as the first ionization energy (I1), is required to overcome the electrostatic forces between the electron and the nucleus. Option b) P(g)+e−→P−(g) describes the addition of an electron to form an anion, not ionization. Option c) P(g)→P−(g)+e+ is incorrect as it implies the production of an anti-electron (e+) or positron in the context of a chemistry setting, which does not occur in ionization reactions. Option d) P(g)+e+→P+(g) suggests that a positron is being added, which again, is not part of a typical ionization process.