This is the 5176th most frequent Japanese word.
酸性
"酸性" means "acidity" or "acidic nature."
The word "酸性" is used to describe the chemical property of the solution as having a pH below 7.
この溶液は酸性です。
This solution is acidic.
Here, "酸性" modifies "雨" (rain), describing the rain as acidic due to dissolved pollutants.
酸性雨は環境に悪影響を及ぼします。
Acid rain negatively affects the environment.
In this case, "酸性" is used as an adjective to describe foods that have acidic properties, affecting digestion.