Which of the following are correct statements? Check all that apply .
A. An atom is the basic unit matter.
B. The atomic number is the number of neutrons an atom has .
C. The number of electrons an atom has defines what kind of element it is
D. An element is defined by the number of protons in its nucleus.

A and D are correct

Explanation:

A is right because an atom is the basic unit of matter.

B is wrong because the atomic number is protons and electrons, not neutrons.

C is wrong because electrons do not determine what element it is, the protons do (this could be right though depending on what your teacher has taught you, but I would say it is wrong. For example, if your teacher says protons and electrons both represent the same thing, then it will be right)

D is right because the atomic number is the protons which is the basis of where it all starts.

ca has a crystalline lattice with positive ions (since it is a metal, metals are positively charged) and electrons flow freely in its structure since the ca atoms have a large nuclear radius so the electrons are not tightly held, therefore the electrons can flow freely since they are not being highly attracted by the nucleus. moreover, one of the properties of metals are that they are conductors of electricity, thus proving ca is the element.