Match List – I with List – II

Choose the correct answer from the options given below:

Correct option is D

Explanation:
Let’s match each chemical with its correct use:
· (A) FeCl₃ → (IV)
· Ferric chloride is a common coagulant used to aggregate suspended particles before sedimentation in water and wastewater treatment.
· (B) Ca(OH)₂ → (III)
· Calcium hydroxide (slaked lime) is used in the soda-lime process to remove water hardness by precipitating calcium and magnesium ions.
· (C) CO₂ → (II)
· Carbon dioxide is added after softening to lower the pH and neutralize excess lime, especially after lime-soda treatment.
· (D) O₂ → (I)
· Oxygen is supplied in the activated sludge process to support aerobic microbial growth during wastewater treatment.
Information Booster:
· Coagulants like FeCl₃ are essential for turbidity removal.
· Ca(OH)₂ reacts with CO₂ to form calcium carbonate in hardness removal.
· Supplying oxygen improves biodegradation efficiency in biological treatment units.
Additional Information:
· Other options mix up functions (e.g., FeCl₃ is not used to promote microbial growth).
· Only Option (4) matches the correct industrial and environmental engineering applications.