Final answer:
Zinc is the metal that serves as the negative pole in batteries, protects iron through plating, and forms brass when alloyed with copper. It is best known for its use in galvanization and batteries, and for forming alloys like brass.
Step-by-step explanation:
The metallic element that serves as the negative pole in the common flashlight battery, is used to plate a protective film on iron objects, and when melted with copper becomes brass is Zinc (Option B). Zinc has a characteristic silvery appearance that tarnishes to a blue-gray color due to a protective coating of basic carbonate that forms on its surface. This coating is an example of passivation, which inhibits further corrosion.
Zinc anodes are widely used in dry cell batteries, including alkaline types. Additionally, roughly half of all zinc production is for galvanizing steel, where a thin layer of zinc protects iron and other metals from corrosion. Brass, which is an alloy of copper and zinc, is also a significant application of zinc.