Im not 100% on these but i can try
1. A compound is made up of elements and their different atoms
2.
A. salt- compound (NaCl) is two elements Na (sodium) and Cl (chloride?)
B. Nitrogen- element its on the periodic table
C. Helium- element its on the periodic table
D. Water- compound (H2O) two elements hydrogen and oxygen
3. element, compound, compound, element
Hope this helps