Can you help me with biology?

1: 46

2: skin?

3:21

4:2nd one

5: last one

hydrogen is a compound or a single element and a element is a pure substence that cannot be separated into simpler subtances

clorine is a compound its a chemical substance that forms when two or more different elements combine

so both hydrogen and clorine are compounds

since there are no options posted i'll give you a few examples.

a dolphin's flipper, bird's wing, cat's leg.