Boron is a ___________.

Hint : To answer this question, we first need to understand what are elements. An element is a pure substance made up entirely of atoms with the same number of protons in their atomic nuclei, as defined by chemistry. Chemical elements, unlike chemical compounds, cannot be broken down chemically into simpler molecules.

Complete Step By Step Answer:
Boron – Boron is a chemical element with atomic number 5 and the symbol B. It is a low-abundance element in the Solar System and the Earth's crust, produced entirely by cosmic ray spallation and supernovae rather than stellar nucleosynthesis. It makes up roughly 0.001% of the Earth's crust by weight.
The water-solubility of its more prevalent naturally occurring forms, the borate minerals, concentrates boron on Earth. Evaporites, such as borax and kernite, are mined industrially. Turkey, the world's leading producer of boron minerals, has the greatest known boron reserves.
Elemental boron is a metalloid that is found in small amounts in meteoroids but is not found naturally on Earth in chemically uncombined form. Because of refractory contamination by carbon or other elements, highly pure boron is difficult to produce in industry. Amorphous boron is a brown powder; crystalline boron is silvery to black in color, highly hard, and a poor electrical conductor at ambient temperature. Boron filaments, which have applications similar to carbon fibers in some high-strength materials, are the most common use of elemental boron.
So, we conclude that boron is a metalloid.

Note :
A metalloid is a chemical element with a majority of properties that fall between those of metals and those of nonmetals, or that are a mixture of the two. There is no universally accepted definition of a metalloid, and there is no consensus on which elements are metalloids. Despite its lack of precision, the word is still used in chemistry literature.