Which of the following metals is used for making jewelry?

Which of the following methods is $NOT$ a method for the refining of metals?

Which type of oxide is $CO_{2}$?

Which alloy is used to prepare surgical instruments?

Explain the following statements:
$(a)$ Most metal oxides are insoluble in water but some of these dissolve in water. What are these oxides and their solutions in water called?
$(b)$ At ordinary temperature,the surfaces of metals such as magnesium,aluminium,and zinc are covered with a thin layer. What is the composition of this layer? State its importance.
$(c)$ Some alkali metals can be cut with a knife.

Which metal is more reactive than magnesium $(Mg)$?