- Matter in gas phase takes the shape of the entire container
- The item takes the shape of the entire container
- So, the item is a kind of matter in the gas phase

- The item is a kind of matter in the gas phase
- Air is a kind of gas
- Therefore, the item is most likely air

Therefore, the item is most likely air
A teacher places an item in a box. The item takes the shape of the entire container. This item is most likely
- Air is a kind of gas 
- Matter in gas phase takes the shape of the entire container 
- The item takes the shape of the entire container