How can you test for hydrogen gas?

To test for hydrogen gas, you can hold a burning splint at the open end of a test tube containing the gas. This method is widely known because hydrogen reacts quickly with oxygen in the air, and it has a distinct characteristic: when hydrogen burns, it produces a 'pop' sound. This audible signal provides a clear indication that hydrogen is present.

The other methods listed do not effectively test for hydrogen. For example, dipping litmus paper into the gas would not provide a reliable test, as hydrogen itself is neutral and would not change the color of litmus paper. Shaking the gas in a closed container would not yield any observable reaction, nor would it validate the presence of hydrogen. While using a gas sensor is a modern method to detect various gases, it is not solely dedicated to hydrogen and would not demonstrate the unique properties of hydrogen through a classic reaction. Therefore, using a burning splint is the most straightforward and traditional method to confirm the presence of hydrogen gas.