Why could the mass of argon be greater than the mass of potassium even though it has a lower atomic number?

The mass given on the periodic table is the weighted average of the abundance of isotopes. Because heavier isotopes (more neutrons) of argon are more abundant than potassium's, by pure statistics, argon will appear with a greater mass on the periodic table.

in easy way

we can also say :- Argon has  greater proportions of heavier isotopes with more neutrons than potassium.

frequency, z, and the collision density, z, in carbon dioxide (co2), r 180 pm at 30 °c and 120 kpa

a 20-cm-long, cylindrical graphite (pure carbon) rod is inserted into an oxidizing atmosphere at 1145 k and 1.013 x 105 pa pressure. the oxidizing process is limited by the diffu- sion of oxygen counterflow to the carbon monoxide that is formed on the cylindrical surface.