0 1 This question is about carbon dioxide. Carbon dioxide is soluble in water and forms an acidic solution. Which ion makes the solution acidic? [1 mark]

## Step 1: The question is asking about the ion that makes a solution acidic when carbon dioxide is dissolved in water.## Step 2: When carbon dioxide (CO2) is dissolved in water (H2O), it forms carbonic acid (H2CO3). ### The chemical reaction can be represented as: ### ## Step 3: Carbonic acid (H2CO3) is a weak acid and it can dissociate in water to form hydrogen ions (H+) and bicarbonate ions (HCO3-).### The dissociation reaction can be represented as:### ## Step 4: The presence of hydrogen ions (H+) in a solution is what makes it acidic. The more hydrogen ions present, the more acidic the solution is.