When sulfur dioxide gas is passed through lime water,which insoluble substance is formed that turns the solution milky?

Which of the following is a noble metal?

Which of the following substances is hygroscopic?

Why do ionic compounds not conduct electricity in the solid state?

Which of the following metals is the least reactive?

Account for the following:
$(a)$ Aluminium is more reactive than iron,but its corrosion is less than iron.
$(b)$ Hydrogen gas is not evolved when zinc metal reacts with dilute $HNO_3$.
$(c)$ Carbon is not used for reducing aluminium from aluminium oxide.