Which of the following ores is in the form of sulphide?

What is ammonium hydroxide $(NH_4OH)$?

About $.......\, \%$ impurity remains in alumina obtained by Bayer's method. (in $\%$)

An element forms an oxide $A_{2}O_{3}$ which is acidic in nature. Identify $A$ as a metal or non-metal.

Name two metals which are purified by electrolytic refining. Mention the anode,cathode and the electrolyte used in the refining process. At which electrode would the pure metal be deposited?

State whether the following statement is true or false:
The elements or compounds,which occur naturally in the earth's crust,are known as minerals.