If an aqueous solution turns blue litmus red, which relationship exists between the hydronium ion and hydroxide ion concentrations?

Answer is: the hydronium ion (H₃O⁺) concentration is greater than hydroxide ion (OH⁻) concentration.

Bases (more hydroxide ions than hydronium ions) turn red litmus paper blue and acids (more hydronium ions than hydroxide ions) turn blue litmus paper red.

Acids and bases have opposite properties and have the ability to neutralize each other. Acids taste sour, give sharp stinging pain in a wound and react with metals to produce hydrogen gas.