Which one of the following is not an ore of aluminium?

The main ore of aluminium is:

$A$ mineral is usually associated with a large amount of unwanted material called

Sulphide ion is a soft base and its ores are common for metals. Which of the following metals commonly occur as sulphide ores?
$(a)$ $Pb$ $(b)$ $Al$ $(c)$ $Ag$ $(d)$ $Mg$
Choose the correct answer from the options given below:

Pyrolusite is......

Which element exists in the free state mainly?