It is a molecule because hydrogen is an element.
An element is made up of molecules
Answer: 
Explanation:
A single displacement reaction is one in which a more reactive element displaces a less reactive element from its salt solution. Thus one element should be different from another element.

Synthesis reaction is defined as the reaction where substances combine in their elemental state to form a single compound.
Decomposition reaction is defined as the reaction where a single substance breaks down into two or more simpler substances.

Combustion is a type of chemical reaction in which hydrocarbons burn in the presence of oxygen to form carbon dioxide and water along with heat.

Answer: Metals form cations.
The alkali metals (the IA elements) lose a single electron to form a cation with a 1+ charge.
The alkaline earth metals (IIA elements) lose two electrons to form a 2+ cation.
Aluminum, a member of the IIIA family, loses three electrons to form a 3+ cation.
Therefore, metals in the s and p block of the periodic table have 1, 2 or 3 electrons in their outermost orbit (or valence shell). Now to gain a stable octet metals lose either 1, 2 or 3 electrons from the valence shell thus forming cation with +1, +2 or +3 charge.
The two oxygen atoms share two pairs of electrons, so two covalent bonds hold the oxygen molecule together