Can someone me with these questions plz

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

D

Explanation:

P.E=mgh

P.E=180×9.8×15

P.E=26 460J