Based on their chemical formulas. State whether the substances tested above are covalent or ionic? need help please

Can someone me with questions 15 to 17 plz.

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

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