Hydrogen is a colorless and less dense gas than air (Among various gases, hydrogen has the smallest density. Under standard conditions, the mass of 1 liter of hydrogen is 0.089 grams, which is much lighter than air for the same volume). Because hydrogen is hard to dissolve in water, it can be collected by drainage gas collection method. In addition, under a standard atmospheric pressure, at a temperature of -252.87 ℃, hydrogen can be transformed into a colorless liquid; at -259.1 ℃, it will become a snow-like solid. At room temperature, the properties of hydrogen are very stable, and it is not easy to chemically react with other substances. But when the conditions change (such as ignition, heating, use of catalysts, etc.), the situation is different. For example, hydrogen has strong activity after being adsorbed by metals such as palladium or platinum (especially adsorbed by palladium). Metal palladium has the strongest adsorption effect on hydrogen. When the volume fraction in the air is 4%-75%, it can cause an explosion when encountering a fire source.

Hydrogen is a colorless and odorless gas with a density of 0.089 g/L (the lightest gas) under standard conditions, and it is difficult to dissolve in water. At -252 ℃, it becomes a colorless liquid, and at -259 ℃ it becomes a snowflake-like solid.