Soda water contains
A. Carbonic acid
B. Sulphuric acid
C. Carbon dioxideD. Nitrous acid

Carbon dioxide

Carbonated water or soda water is water containing dissolved carbon dioxide gas, either artificially injected under pressure or occurring due to natural geological processes. Carbonation causes small bubbles to form, giving the water an effervescent quality.
Carbonated water has benefits for digestion. It may improve swallowing, increase feelings of fullness and reduce constipation. Many people believe that carbonated beverages are bad for bones because of their high acid content. However, research suggests the carbonation isn't to blame.
Chemically, carbonated water is better known as carbonic acid that has simply been created by pumping carbon gases into water.(H2CO3)