D. a compound. The protons and neutrons make up most of the size of the atom. Each atom of an element has the same mass number. An ion is formed by the loss or gain of electrons. Ionic compounds will conduct electricity in the solid form.
Most molecular compounds are hard, brittle substances at room temperature.
The majority of elements in the periodic table are classified as metals. Most ionic compounds will dissolve in water. A. 1 and 3 B. 1 and 2 C. 2 and 4 D. 3 and 4 7. The formula for the ionic compound dinitrogen pentoxide is N 2 O 5 . The formula for the ionic compound phosphorus tribromide is PBr 3 . 9.