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

Metals are refined by using different methods. Which of the following metals are refined by electrolytic refining?
$(i)$ $Au$
$(ii)$ $Cu$
$(iii)$ $Na$
$(iv)$ $K$

$(a)$ 'Sodium is a highly reactive metal and it cannot be obtained from its oxide by heating with carbon'. Give reason.
$(b)$ How can sodium be obtained from sodium chloride?

Which metal ore can be concentrated by the magnetic separation method?

Name the metal which:
$(a)$ becomes blackish after a certain time.
$(b)$ develops a green coating on exposure to air.
$(c)$ does not corrode at all.
$(d)$ is used in making steel.
$(e)$ is non-lustrous.

What type of compounds are formed when reactive metals like sodium and potassium react with dihydrogen?