A student looks up an element on the periodic table. The table says that the atomic number of the element is 12 and the mass number of the element is 40. What information do these two numbers convey about the element?
a
The element has 40 protons and 12 neutrons
b
The element has 12 protons and 12 neutrons
c
The element has 12 protons and has 28 neutrons
d
The element has 28 protons and 40 neutrons
The correct answer is a) The element has 40 protons and 12 neutrons.
The atomic number of an element represents the number of protons it has in its nucleus. In this case, the element has 12 protons.
The mass number of an element represents the total number of protons and neutrons in its nucleus. In this case, the element has a mass number of 40, which means it has 12 protons and (40 - 12 =) 28 neutrons.