Select the most appropriate meaning of the given idiom.

On cloud nine

Extremely happy

The most appropriate meaning of the idiom "on cloud nine" is extremely happy. It is an informal expression that means to be in a state of great happiness and elation. The idiom is thought to have originated in the early 1900s, and the exact meaning of the phrase is unknown. However, it is believed to be a reference to the feeling of being carefree and happy, like being floating on a cloud.

The other options for the meaning of the idiom are incorrect. Flying with a parachute is not an idiom, and it does not mean to be extremely happy. Frequently flying by air is also not an idiom, and it does not mean to be extremely happy. Extremely sad is the opposite of extremely happy, so it is also not the correct meaning of the idiom.