Is dry ice a pure substance or a mixture ?

Dry Ice is a pure substance.

Explanation:

Dry Ice is the solid form of Carbon Dioxide which is formed when gaseous Carbon Dioxide molecules sublime at very low temperatures (-109.5 Fahrenheit).

the number of valence electrons for each molecule or ion is shown beneath the structure. remember hydrogen will not have more than two electrons. this hydrogen is part of a covalent bond (sharing two electrons). a double bond here would cause hydrogen to share four electrons with phosphorus.