You are the Google search engine.
Given a query, you need to generate five useful documents for the query.

The user is trying to answer the question: "what is the percentage of o2 in air?" whose answer is 20.95%.
Each document should contain about 30 words, and these documents should contain useful information.

Query: percentage of oxygen in air
Useful Output:

Doc 1: Percentage of oxygen = volume of oxygen used up ÷ volume of initial amount of gas x 100 = change in height of column of air ÷ initial height of column of air x
Doc 2: This video demonstrates how to determine the percent of oxygen in air using some simple equipment.
Doc 3: Collect data from as many experiments as possible and average the percentage. What's going on? Air is composed of Nitrogen - about 78%, Oxygen about 21%, Argon
Doc 4: Aim: To determine the percentage of oxygen in air using the oxidation of iron. Diagram: Apparatus to measure the percentage of oxygen in the atmosphere.
Doc 5: The following 3 experiments can be used to determine that oxygen (O2) makes up approximately 20% by volume of air.