Position in the periodic table and predicting properties

Lithium, sodium, and potassium are all in Group 1, also called the alkali metals. Elements in the same group share similar chemical and physical properties.

Group 1 metals are characterised as soft, shiny metals with low density — so low that lithium, sodium, and potassium all float on water.

Hard, dense metals with high melting points describe transition metals, not Group 1. Group 1 metals are highly reactive with water, so they are definitely not non-metals.

The correct answer is that they are soft, shiny metals with low density. This is a defining characteristic of Group 1 alkali metals.

We need to find the property that all three Group 1 elements — lithium, sodium, and potassium — share.

Hard and dense metals with high melting points describes transition metals like iron or copper, not Group 1 metals. Sodium, for example, melts at only 98 °C.

Lithium, sodium, and potassium are metals, and they all react vigorously with water. This option is completely wrong on two counts.

Forming coloured compounds is a characteristic of transition metals (e.g. copper sulfate is blue). Group 1 compounds are generally colourless or white.

By elimination, the answer is soft, shiny metals with low density — the defining features of Group 1 alkali metals.

Elements on the right-hand side of the periodic table are non-metals. The staircase-like line marks the boundary between metals and non-metals.

Non-metals generally have opposite properties to metals: they tend to be dull, brittle when solid, and poor conductors of heat and electricity.

The answer 'dull appearance, brittle when solid, poor conductor of electricity' matches the expected properties of a non-metal perfectly.

We need to predict properties for an element on the right-hand side of the periodic table, which places it in the non-metal region.

Shiny, malleable, and good conductor are properties of metals, which are on the left-hand side, not the right.

Soft, low-density metal that reacts with water describes a Group 1 metal — also found on the left side of the table.

Hard, dense, high melting point, forms coloured compounds describes transition metals, which are in the middle of the table.

The remaining option — dull, brittle, poor conductor — correctly describes a non-metal on the right-hand side.