Question

1. an atom has 18 protons, 18 electrons, and 20 neutrons. this atom has

a positive charge
a negative charge
a mass number of 38
an atomic number of 20

Explanation:

Step1: Calculate the charge

The charge of an atom is calculated by the formula \(Charge = \text{Number of protons}-\text{Number of electrons}\).
Given that the number of protons \(= 18\) and the number of electrons \(= 18\), then \(Charge=18 - 18=0\). So, the atom has no positive or negative charge.

Step2: Calculate the mass number

The mass number (\(A\)) of an atom is given by the formula \(A=\text{Number of protons}+\text{Number of neutrons}\).
Given that the number of protons \(= 18\) and the number of neutrons \(= 20\), then \(A = 18+20=38\).

Step3: Determine the atomic number

The atomic number (\(Z\)) of an atom is equal to the number of protons.
Given that the number of protons \(= 18\), so the atomic number \(Z = 18\), not \(20\).

Answer:

a mass number of 38