Inside Atom

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Across
  1. 3. Which is the central core of the atom?
  2. 4. counter Radiation is detected by an instrument called _____________ _____________.
  3. 7. Which isotope contains 2 neutrons a)protium b)deuterium c)tritium?
Down
  1. 1. The first radioactive element is discovered by whom?
  2. 2. What is the mass atomic number of proton?
  3. 5. What is the maximum number of electrons that can fit into the second shell of an atom?
  4. 6. Positively charged particle is ____________.