Boron, silicon, germanium, arsenic, antimony and tellurium are examples of:

Metalloids, also called semi-metals, are elements whose properties lie between those of metals and non-metals. They have some properties of metals (for example, a metallic lustre) and some of non-metals (for example, they are brittle and are not good conductors like metals).

The elements usually classified as metalloids are boron (symbol B), silicon (Si), germanium (Ge), arsenic (As), antimony (Sb) and tellurium (Te). Polonium (Po) and astatine (At) are sometimes included.

In the modern periodic table, metalloids lie along a diagonal "staircase" line that separates the metals on the left from the non-metals on the right.

Properties of metalloids:

• They are solids at room temperature.
• They often have a shiny, metallic appearance but are brittle and break easily.
• Many are semiconductors: their electrical conductivity is intermediate, and it increases with temperature (unlike metals, whose conductivity decreases on heating).
• They can form alloys with metals.
• Their oxides are often amphoteric or weakly acidic.

Uses of metalloids:

• Silicon and germanium are used in semiconductors, transistors, computer chips and solar cells.
• Boron is used in borosilicate glass (such as Pyrex), in control rods of nuclear reactors to absorb neutrons, and as borax and boric acid.

Arsenic is used in some semiconductors (gallium arsenide) and was used in pesticides; it is highly poisonous. Arsenic contamination of groundwater is a serious problem in West Bengal, Bihar and Bangladesh.

Antimony is used in alloys, flame retardants and batteries.

Tellurium is used in solar panels (cadmium telluride) and alloys.

Why not the other options?

• ✗Noble gases, such as helium, neon and argon, are in Group 18 and are very unreactive.
• ✗Alkali metals, such as lithium, sodium and potassium, are in Group 1 and are highly reactive.
• ✗Transition metals, such as iron, copper and zinc, are in the d-block.