Yes it can
An element - substance - NOT a mixture.
a mixture
Neither. Oxygen is an element, which is a pure substance and not a mixture.
pure substance
I think it's a mixture.
Copper metal is an element and thus a pure substance.
copper is a substance
Sodium is a pure substance, an Element.
Fluorine is certainly a substance, it is an element.
Molybdenum is an element, so it is a substance.
Hydrogen is not a mixture at all. It is an element and therefore a pure substance.
Sulfur is not a mixture at all. It is a pure substance. Specifically it is an element.