Which of the following metal is the most difficult to extract from its oxide?

Which of the following is most difficult to detect :-

Which of the following is most difficult to oxidise ?

Which out of the following metal oxides is the most acidic?

Which of the following ore is/are extracted from its oxide by sir reduction method

Carbon and CO gas are used to reduce which of the following pairs of metal oxides for extraction of metals ?

Describe the role of the following: Coke in the extraction of iron from its oxides.