Only electrically neutral atoms.
Atoms of the same kind. To be more precise, all atoms in an element have the same number of protons (but not necessarily the same number of neutrons - do some reading on "isotopes" for more details).
Atoms are made of protons, neutrons and electrons.
A neutral atom has no electrical charge on it. So the number of protons in the nucleus is equal to the number of electrons surrounding it. In their normal, elemental state, all atoms are neutral. If it's in an ionised solution, say, then it's not neutral. I think there's something more to your question, though. Why are you asking - is there a situation or a kind of atom that you are thinking of?
They have the same chemical formula and the same properties when in their pure state. Atoms of the same element have the same number of protons. This is the atomic number which is unique to each element and is on the periodic table. The number of protons in the nucleus defines the element. In a neutral atom, the number of electrons are also the same.
The number of protons in the nucleus will ALWAYS be the same for a specific element.(ex: Hydrogen always has EXACTLY 1 proton)But, the number of electons and neutrons can vary in a particular element.
Zinc has 30 protons since its atomic number is 30. This also means that it has 30 electrons to balance the positive charge from the protons. The number of neutrons in an atom of zinc can vary based on the isotope, but a typical zinc atom has around 35 neutrons.
Sodium has 11 positively charged protons. (All atoms have positively charged protons, though they differ in hte number of protons).
That's called an element. The 90 or so naturally occurring elements, in various combinations, make up all matter in the universe.
all atoms of the same kind of matter have the same number of protons in them. 🙈
They have the same number of protons in their nuclei.
What do you mean by "normal" atom? There are ions: charged atoms or molecules. It is charged because the number of electrons do not equal the number of protons in the atom or molecule. An atom can acquire a positive charge or a negative charge depending on whether the number of electrons in an atom is greater or less then the number of protons in the atom. But I think a "normal" atom, would be a neutral one. A neutral atom has the same amount of protons as electrons, therefore have no net charge.