The matter

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Across
  1. 4. the total number of protons and neutrons in a nucleus
  2. 7. the central and most important part of an object, movement, or group, forming the basis for its activity and growth
  3. 9. a atomic particle that occurs in the nucleus of every atom and carries a positive charge equal in size to the negative charge of an electron
  4. 10. a uncharged atomic particle that has a mass nearly equal to that of the proton and is present in all known atomic nuclei except the hydrogen nucleus
Down
  1. 1. a substance that cannot be broken down into simpler substances by physical or chemical means
  2. 2. equal to the number of protons in the nucleus of an atom
  3. 3. an atom or molecule with a net electric charge due to the loss or gain of one or more electrons
  4. 5. a negatively charged subatomic particle that can be either bound to an atom or free
  5. 6. atoms with the same number of protons and electrons, but a different number of neutrons
  6. 8. anything that has volume and mass