Element $Z$ is a lustrous, ductile solid that is an excellent conductor of electricity.

Classify Element $Z$ as either a metal or a non-metal.

Compare the physical properties of metals and non-metals, explaining the differences in their electrical conductivity, malleability, and melting and boiling points in terms of their structure and bonding.

Potassium ($K$, atomic number 19) is a Group 1 alkali metal, while Argon ($Ar$, atomic number 18) is a Group 0 noble gas.

Explain, with reference to their electronic configurations, why potassium is extremely reactive whereas argon is highly stable and unreactive.