Which one of the following is the correct sequence of the given substances in the decreasing order of their densities?

Which one of the following is the correct arrangement of metals in the decreasing order of their reactivity?

Which one of the following is the correct reactivity series with water?

Which of the following is not correctly matched?

Which one of the following is essential in corrosion of iron metal?

Which one of the following metals floats in cold water?