What can you say about a calcium atom by looking at the symbol

The symbol for calcium is "Ca" and its atomic number is 20. This means that a calcium atom has 20 protons. The most common isotope of calcium has a mass number of 40, calculated as the sum of protons and neutrons.

To find the number of neutrons, you can subtract the number of protons from the mass number:

- Mass number (40) - Number of protons (20) = Number of neutrons (20).

With this information, we can evaluate the options:

A. A calcium atom has 44 neutrons and 20 electrons.
**Incorrect** - A calcium atom has 20 neutrons.

B. A calcium atom has 20 protons and 24 electrons.
**Incorrect** - A neutral calcium atom has equal numbers of protons and electrons, so it has 20 electrons.

C. A calcium atom has 64 protons and 20 neutrons.
**Incorrect** - A calcium atom only has 20 protons.

D. A calcium atom has 20 protons and 24 neutrons.
**Incorrect** - A calcium atom typically has 20 neutrons (not 24).

E. A calcium atom has 20 protons and 44 neutrons.
**Incorrect** - A calcium atom has 20 neutrons (not 44).

Based on the above analysis, none of the provided options correctly describe a typical calcium atom, which has 20 protons, 20 neutrons, and 20 electrons in its most common isotope (Ca-40).