During a chemistry demonstration, a teacher adds small, equal-sized pieces of lithium, sodium, and potassium to separate troughs of water.
Only the reaction involving potassium consistently produces a flame (which burns with a distinctive lilac colour).
Which statement best explains why a flame is produced only with potassium?
Potassium is less dense than sodium and lithium, so it floats higher in the air.
Potassium is more reactive, releasing heat energy fast enough to ignite the hydrogen gas produced.
Potassium has a higher melting point, so it does not melt and is able to catch fire as a solid.
Potassium is the only one of the three metals that reacts with water to produce a gas.
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.