Final answer:
Bromine is the most active non-metal in period 4 due to its low ionization energy, which facilitates the gain of an electron to form a stable anion, and its position in group 17 as a halogen which is highly reactive.
Step-by-step explanation:
The question asks why bromine is the most active non-metal in period 4. The most active non-metals are halogens found in group 17 of the periodic table. These elements are highly reactive because they are strong oxidizing agents and have a high tendency to gain electrons to fill their valence shell to achieve a noble gas configuration. Bromine, being a halogen, is no exception and is the only non-metal of period 4 in group 17. Its reactivity can be attributed to its low ionization energy, which makes it easier for bromine to gain an electron and form a stable anion with a configuration similar to the noble gas krypton.
The three primary factors that would support bromine's reactivity are its position in the periodic table in group 17, its desire to gain an electron to achieve noble gas electron configuration, and the general trend that non-metallic character increases across a period. While bromine's atomic number and atomic radius do influence its properties, these are not the direct reasons for its high reactivity. Instead, its low ionization energy and the fact that it is a halogen play the key roles. Thus, the correct answer to the question is (c) As a result of its low ionization energy.