Explain the trends in metallic character and reactivity of elements, and the properties/uses of specific elements and their compounds.

a)
Element: L
Reason: Metallic character increases down a group and decreases across a period. Element L is positioned lower in Group I than K, making it more metallic than K. Group I elements are generally more metallic than Group III elements, where P is located. Therefore, L is the most metallic.

b)

(i) One use of element S (a noble gas) is in lighting, for example, in neon signs or as an inert atmosphere in light bulbs.

(ii) Some metals, particularly heavy metals like lead or mercury, are harmful to humans because they are toxic. They can accumulate in the body over time, interfering with biological processes, damaging organs such as the brain, kidneys, and liver, and disrupting enzyme function.

a)

(i) The metals arranged in increasing order of reactivity (least reactive at the top, most reactive at the bottom) are:
Gold
Lead
Iron
Aluminium
Sodium

(ii) From the list, the metal whose metal hydroxide does not undergo thermal decomposition is Sodium. Sodium hydroxide is thermally stable.