Are there some elements on the periodic table that hasn't been discovered?

Which element is the least metallic between cadmium, silver, zinc, or iron?

Iron (3) oxide will decompose in the presence of hydrogen gas and heater to produced iron and digydrogen monoxide white a balanced chemical equation

Acm ruler with main graduations from 1 to 10 from left to right there are 10 secondary graduations between each of the main graduations there is a line that begins. at the left end of the ruler 10 secondary graduations to the left of the “1 main graduation the right end of the line ends on the eighth secondary graduation to the right of 3 how long is the line