What is the colour of lithium in a flame test?

• A yellow
• B crimson-red
• C lilac
• D green

The trend in the first ionisation energies for these elements is opposite to the trend in their atomic radii.

Predict a value for the first ionisation energy of rubidium.

Caesium is another element in Group 1, located below rubidium.

Predict its atomic radius and how its reactivity compares to rubidium.

• Atomic radius: $.............pm$
• Reactivity: $.............$

Group 1 elements exhibit very similar chemical properties. This similarity is primarily because their atoms all possess the same number of:

• A protons in the nucleus
• B electrons in their outermost shell
• C neutrons in their most common isotope
• D fully filled electron shells

A student wrote these statements about the reactions of the Group 1 elements.

• The melting point of the alkali metals increases down the group.
• When potassium reacts with water, a lilac flame is observed.
• The chemical formula of sodium chloride is $NaCl$.
• The equation for the reaction of potassium with oxygen to form its oxide is $4Li+O_2\to 2{Li}_{2}O$.
• In the redox reaction between lithium and water, lithium acts as an oxidising agent.

Three of the statements contain one incorrect word.

Complete the table to show each incorrect word and the correct word that should be used to replace it.