Problem: What is the molecular weight of oxygen?

We are asked to find the molecular weight of Oxygen. 

Molecular weight is simply the weight or mass of 1 mole of a molecule.  It is equal to the molar mass, given by the equation.  

$\boxed{\mathbf{Molecular}\mathbf{ }\mathbf{weight}\mathbf{ }\mathbf{=}\mathbf{ }\mathbf{Molar}\mathbf{ }\mathbf{Mass}\mathbf{ }\mathbf{=}\mathbf{ }\mathbf{atomic}\mathbf{ }\mathbf{mass}\mathbf{ }\mathbf{\times }\mathbf{ }\mathbf{\#}\mathbf{ }\mathbf{of}\mathbf{ }\mathbf{atoms}\mathbf{ }\mathbf{\left(}\mathbf{subscript}\mathbf{\right)}\mathbf{ }\mathbf{in}\mathbf{ }\mathbf{the}\mathbf{ }\mathbf{molecule} }$

Recall that oxygen is diatomic, which means that it exists as O₂ instead of O.  It is considered a molecule because it is composed of 2 elemental Oxygens.