What happens when copper oxide is heated in the presence of dihydrogen gas?

$A$ mixture of equal amounts of $H_2$ and $Cl_2$ gases in a gas jar produces white fumes in the absence of sunlight. What are these white fumes?

Food cans are coated with tin and not with zinc because:

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.

On which principle does the method of fractional distillation work?

Write true or false for the following statement:
Hydrogen gas is evolved when a metal reacts with nitric acid.