Ionic compounds. because when in solid form they are held firmly in place therefore they cannot move to conduct electric current.
I think Magnesium not sure because the relative atomic mass of magnesium is 24,31.
I think the correct answer from the choices listed above is the last option. The formula for phosphorous acid is H3PO3. It <span>also called orthophosphorous acid, one of several oxygen acids of phosphorus, used as reducing agent in chemical analysis. Hope this answers the question.</span>