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.

so here we go

atomic mass

239 + 1 = y + 134 + 3 combine like terms

240 = y + 137             subtract 137 from both terms

240 - 137 = y

103 = y

atomic number

94 = z +54 + 0

94 = z + 54               subtract 54 from both sides.

40 = z

answer

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