Question

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

Answer 1

c
The atomic number is 12 so it has 12 protons.
The mass number = 40 = number of protons + number of neutrons
40 = 12 + number of neutrons or # neutrons must be 28.