Question

Which of the following materials is hard, opaque and shines when freshly cut?
(A) Rubber
(B) Wood
(C) Tin
(D) Plastic

Answer 1

As we know that materials or substances are mainly categorized as metals, non-metals and semiconductors. Metals are those materials or substances that are hard, have good tensile strength and are good conductors of heat and electricity whereas non-metals are not hard enough and also bad conductors of heat and electricity. Semiconductors have properties intermediate between metals and non-metals.

Complete answer:
Let us first discuss the properties of metals and non-metals as follows:-
-Metals: These are those substances or materials which are hard and have a high tensile strength. These are solid at room temperature and also good conductors of heat and electricity. These are malleable, that is they can be beaten into thin sheets.
-Metals can be drawn into thin wires which mean metals are ductile. They generally have high melting and boiling points. These are opaque and are mostly silvery grey. They have a lustrous (shiny) appearance.
Few examples of metals are: iron, tin, copper, silver, etc.
-Non-metals: These are those substances or materials which are not as hard as metals and have a high tensile strength. These are bad conductors of heat and electricity and also these are not malleable as well as ductile. They don’t have any shiny appearance.
Few examples of non-metals are: rubber, plastic, wood, carbon, etc.

Therefore the material which is hard, opaque and shines when freshly cut is (C) Tin.

Note:
Few exceptions are as follows:-
-Caesium (Cs) and Gallium (Ga) have low melting and boiling point even after being a metal. Similarly mercury is liquid in state. Sodium and potassium are so soft that they can be easily cut down even by a knife.
-Diamond, being a non-metal, is a very hard substance and graphite is a good conductor of electricity.