Question

A neutral atom of potassium (K) has an average mass of 39 amu and 19 electrons. How many neutrons does it have?

10
19
20
58

Answer 1

I think it is 58, am I correct?

Answer 2

I mean 20, sorry

Answer 3

remember that mass # is protons + neutrons,
and for a neutral atom, # protons = # electrons

so since you have 19 electrons you have 19 protons

39 - 19 = 20, so yes, 20

Answer 4

Thank you!