Answer:
Option A is correct. oxygen gas
Explanations
What is a solution?
A solution is a mixture (homogenous in nature) of two or more substances.
According to the question, we are to determine which of the options is not considered as a solution.
Air is categorized as a solution since it is made up of different gases.
Orange popsicle and lemonade are also a homogenous mixture of different substances, hence they are considered a solution
The only element that is not considered as a solution is oxygen gas being a gas. Therefore the correct option is oxygen gas.