The metallic constituents of hard water are

A. Calcium, magnesium and iron

B. Magnesium, Calcium and tin

C. Magnesium, tin and iron

D. Iron, tin and calcium

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  2. In an atomic nucleus, neutrons and protons are held together by
  3. Apparatus invented by Archimedes is :
  4. The most important ore of Aluminium is
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  6. Permanent hardness of water, due to sulphates of the metal, can be destroyed by the use of
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  14. What is the unit for measuring the pitch or frequency of sound ?
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  18. The metal used in storage batteries
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  20. The type of glass used in making prisms and lenses is
  21. Which of the following elements is non-radioactive?
  22. The recent atomic weight scale is based on
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  26. The formula of Plaster of Paris is
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