Aneutral atom of potassium (k) has an average mass of 39 amu and 19 electrons. how many neutrons does it have? a. 10 b. 19 c. 20 d. 58

20

Explanation:

In a neutral atom, the number of protons (p) equals the number of

electrons (e).

p = e

e = 19, so

p = 19

The mass number (A) is the number of protons plus the number of

neutrons (n).

 A = p + n

 A = 39, so

39 = 19 + n     Subtract 20 from each side.

  n = 20

The atom has 20 neutrons.

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the answer is barium and copper bromide