Classify the following items as either metal or nonmetal: oxygen, aluminum, sulfur, sodium.
Oxygen - nonmetal
Aluminum - metal
Sulfur - nonmetal
Sodium - metal
Complete the following task based on the instruction and optional input provided.### Instruction:
Classify the following items as either metal or nonmetal: oxygen, aluminum, sulfur, sodium.

### Output:
Oxygen - nonmetal
Aluminum - metal
Sulfur - nonmetal
Sodium - metal