Today, about 120 chemical elements are known but only 103 out of them are well characterized in terms of their properties. The systematic classification of these 103 elements reveals that 90 elements are solids, 2 are liquids and 11 are gases. Further, 79 of them are metals, 17 are non-metals and 7 are metalloids. Metals differ from non-metals in many respects. In fact, metals and non-metals are two extremes as regards their properties. Metals occupy the bulk of the periodic table, while non-metallic elements can only be found on the right-hand-side of the Periodic Table. A diagonal line, drawn from boron (B) in group 3 (or 13) to polonium (Po) in group 6 (or 16), separates the metals from the non-metals. Most elements on this line, or often to its immediate left are metalloids, or metal-likes. Elements to the lower left of this division-line are called metals, while elements to the upper right of this division-line are called non-metals. On the basis of their general physical and chemical properties, every element in the periodic table can be termed either a metal or a non-metal.
The elements in group 3 (or 13) of the periodic table are boron, aluminum, gallium, indium and thallium. Among them, boron is a metalloid and the remaining elements which lie to the left of the diagonal line referred to above, are metals.
On this basis, Indium can be safely classified as a metal.