I need help understanding those 3 questions. Can you explain your answer for each of them please.

The solid compound, Na3PO4 contains A. Na+,P5+, and O2 ions B. Na+and PO43 ions C. Na3+ and PO43 ions D. Na3PO4 molecules Keywords: ion, cation, polyatomic ion, ionic compound, covalent bond, charge neutral Concepts: ionic compounds B C A D What is the percent by mass of phosphorus in tetraphosphorus decoxide? Keywords: compound, percent composition, molecular compound, pure substance, molar mass, chemical formula Concepts: Pure substance, % by mass, \begin{tabular}{|c|} \hline 10.9% \\ \hline 56.3% \\ \hline 21.8% \\ \hline 43.7% \\ \hline \end{tabular} Question 4 The correct chemical name for the compound HIO is Keyword: hydrogen ion, polyatomic ion, acid, prefix, suffix Concepts: inorganic-compound nomenclature, systematic naming of acids hypoiodous acid hydrogen iodide oxide periodic acid hydrogen iodite