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.

- lead + phosphoric acid = hydrogen + lead(ii) phosphate

dynamic equilibrium is the answer.