A student adds a small piece of potassium metal to a beaker of water containing a few drops of phenolphthalein indicator. Which option correctly identifies the observations made and provides the correct explanation for the difference in reactivity between potassium and sodium?
The solution turns pink, hydrogen gas is evolved, and potassium is more reactive than sodium because its outer electron experiences greater shielding and is lost more easily.
The solution turns pink, oxygen gas is evolved, and potassium is more reactive than sodium because its higher nuclear charge attracts the outer electron more strongly.
The solution remains colourless, hydrogen gas is evolved, and potassium is more reactive than sodium because its smaller atomic radius allows water molecules to coordinate more closely.
The solution turns blue, hydrogen gas is evolved, and potassium is less reactive than sodium because its valence electron is held more tightly by its larger nucleus.
75 exam-style questions on Edexcel GCSE Chemistry 7.1 Group 1, covering 7.1.1 Classifying elements by group in the periodic table and 7.1.2 Properties and reactions of the alkali metals. Each one has a worked solution and a mark scheme showing where the marks go.