Periodic table

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Across
  1. 3. used in water and swimming pools as a disinfectant
  2. 5. crucial for bones
  3. 7. tin foil is made of this
Down
  1. 1. the element that we breathe that is also needed for respiration
  2. 2. a component of table salt
  3. 4. used in balloons to allow them to rise
  4. 6. commonly used in toothpastes