🔍 Key Concepts

• Boiler water chemistry and common dissolved gases • How oxygen and other gases cause pitting and general corrosion in steel • Difference between alkaline vs acidic gases in water and their effect on metal surfaces

💭 Think About

• Think about which gas, when dissolved in water, tends to form an acidic solution that attacks metal and worsens oxygen corrosion in boilers. • Consider which of these substances is commonly discussed in boiler water treatment, along with oxygen, in engineering and marine engineering texts. • Ask yourself which of these gases is typically removed or neutralized using de-aeration and chemical treatment (like adding alkali or amines) in boiler systems.

✅ Before You Answer

• Verify which option forms carbonic or other acids when dissolved in water and exposed to heat/pressure. • Check marine engineering references on "oxygen and _______ corrosion" in boiler tubes and drums. • Eliminate choices that are less commonly associated with standard boiler water treatment discussions on dissolved gases.