Patterns of properties to organise elements

Physical properties describe how a substance looks or behaves without changing into a different substance — e.g., melting point, density, appearance. Chemical properties describe how a substance reacts with other substances to form new substances.

Melting point, density, and appearance (shiny or dull) can all be measured without causing a chemical reaction — these are physical properties. Reacting with water involves a chemical change, so it is a chemical property.

How vigorously it reacts with water is a chemical property because it describes the element's behaviour during a chemical reaction, not just its physical state.

The question asks for a chemical property, meaning a property that involves how an element reacts chemically with something else.

Melting point is the temperature at which a solid turns to liquid. No new substance is formed — this is a physical property, not a chemical one.

Appearance (shiny or dull) can be observed without any chemical reaction occurring. This is a physical property.

Density is mass per unit volume, which can be measured without any chemical change. This is a physical property.

How vigorously it reacts with water is the only option that involves a chemical reaction, making it a chemical property.

The element is: shiny (lustrous), solid at room temperature, conducts electricity, and is malleable (can be hammered into sheets without breaking).

Typical metal properties include: shiny appearance, solid at room temperature, good electrical conductivity, and malleability. All four properties listed in the question match metal characteristics.

Because all the described properties are consistent with metals — and none suggest non-metal or metalloid behaviour — the element is best classified as a metal.

The question asks us to classify an element based on its properties: shiny, solid, conducts electricity, malleable.

Noble gases are all colourless gases at room temperature. This element is a solid, so it cannot be a noble gas.

Non-metals are typically poor conductors of electricity and solid non-metals are often brittle — not malleable. This element conducts electricity and is malleable, so it is not a non-metal.

Metalloids share some properties of both metals and non-metals. Silicon, for example, is a semiconductor but is brittle. This element is fully malleable and a good conductor, which points strongly away from metalloid.

All properties match those of a metal: shiny, solid, good conductor, and malleable.