Question

What is the mass number of an atom of potassium that has 20 neutrons?

1) 15
2) 19
3) 35
4) 39
5) 59

Answer 1

The mass number of a potassium atom with 20 neutrons is 39, which is the sum of its 19 protons and the 20 neutrons in its nucleus.

Step-by-step explanation:

The question is asking about the mass number of a potassium atom with 20 neutrons. Potassium (K) has an atomic number of 19, meaning it possesses 19 protons. The mass number is the sum of protons and neutrons in an atom. Using the given information, we can calculate the mass number as follows: mass number = number of protons + number of neutrons = 19 + 20 = 39. Therefore, the mass number of a potassium atom with 20 neutrons is 39.