Which of the following is a characteristic of a reversible reaction?

When a chemical reaction is progressing:

Write the difference between homogeneous equilibrium and heterogeneous equilibrium.

$A$ reversible reaction is one which

The reaction $3Fe_{(s)} + 4H_2O_{(g)} \rightleftharpoons Fe_3O_{4(s)} + 4H_{2(g)}$ becomes reversible when it is performed in ................

Which of the following processes are reversible?
$I$. Vaporization of a liquid at its boiling point.
$II$. Expansion of gas into vacuum.
$III$. Transformation of a solid substance into liquid at its melting point.
$IV$. Neutralization of an acid by a base.