It is a compound because it is made of oxygen, hydrogen and other elements.
Neither. Air is a mixture. Also, whether something is a compound or an element does not depend on temperature.
Magnesium is a chemical element, not a compound.
Copper is a chemical element. It can be a compound but copper is usually known as a chemical element.
Radium is a chemical element; a compound has a minimum of two chemical elements.
Radium is a chemical element, not a compound.
Silver is a metalic chemical element.
Sodium is a chemical element. Salt is a compound of sodium and chlorine.
I2 is an Element. It is the chemical symbol for molecular iodine.
Iodine is a chemical element; not a mixture, not a compound.
Potassium is a chemical element.
Helium (He) is a chemical element, not a compound; the chemical symbol is He.
Neon (Ne) is a chemical element, not a compound.