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By losing two electrons ,the calcium atom forms a calcium ion( Ca^2+ )  ,and by gaining two electrons ,the oxygen atom forms an oxide ion (O^2-).The calcium ion has 2 units positive charge whereas the oxide ion has 2 units negative charge ,which are held together by strong electrostatic force of attraction to form calcium oxide compound Ca²⁺O^2-  .Thus calcium oxide contains ionic bonds .The electron dot representation for the formation of calcium oxide is shown below ,

(ii) Bronze is a metal alloy consisting primarily of copper usually with tin as the main additive .It is hard and brittle .