Explain why the relative atomic mass of argon is greater than the relative atomic mass of potassium, even though the atomic number of potassium is greater than the atomic number of argon.

Deduce the numbers of protons and electrons in the \({{\text{K}}^ + }\) ion.

argon has a greater proportion of heavier isotopes / OWTTE / argon has a greater number of neutrons;

19 protons and 18 electrons;

This question was the best answered on the paper and generally well answered question. In part (a) candidates sometimes incorrectly used the term relative atomic mass instead of relative isotopic mass when referring to the mass of an isotope.

Most candidates correctly deduced the number of protons and electrons in the \({{\text{K}}^ + }\) ion, however some candidates did not read the question carefully and deduced the number of subatomic particles in the K atom.