* Hydrogen (H2): Around 80%

* Helium (He): Around 19%

These are the two most abundant elements in the universe and make up the bulk of Neptune's atmosphere.

In addition, there are trace amounts of:

* Methane (CH4): This is what gives Neptune its distinctive blue color. It absorbs red light and reflects blue light.

* Ammonia (NH3): Found in small amounts.

* Water (H2O): Present in trace amounts, but it's believed to be the most abundant ice in the deep atmosphere.

* Hydrogen sulfide (H2S): A possible contributor to the planet's blue color.

Key points to remember:

* No solid surface: Neptune doesn't have a solid surface like Earth. Instead, its atmosphere gradually blends into its interior.

* Windy and dynamic: Neptune has the strongest winds in the solar system, reaching speeds of over 2,000 kilometers per hour.

* The Great Dark Spot: Similar to Jupiter's Great Red Spot, Neptune has a persistent storm called the Great Dark Spot. These storms are giant whirlpools that can last for months or years.

Overall, Neptune's atmosphere is a complex and dynamic environment. It is characterized by its fast winds, deep clouds, and the presence of various elements and compounds.