Answer:
Carbonic
Step-by-step explanation:
Rain water is slightly acidic with a pH of 5.6. This happens due to the rain water reacting to atmospheric Carbon dioxide in atmospheric concentrations.
H20+ CO2= H2CO3 (carbonic acid)
The Hydrogen ions in the H2CO3 ( weak Carbonic acid) makes the water acidic. This explains the reason why rain water is referred to as acidic water.