Step 1: Understanding the Question:
The question asks to identify the chemical reactant that pozzolanic materials (like Fly Ash or Silica Fume) react with in Portland Pozzolana Cement (PPC).
Step 2: Detailed Explanation:
The Hydration of OPC: When standard Portland cement hydrates, the silicates $(C_3S, C_2S)$ react with water to form C-S-H gel (which provides strength) and a byproduct: Calcium Hydroxide, also known as Lime ($Ca(OH)_2$).
Problem with Lime: This liberated lime does not contribute to strength and is actually a weakness, as it is soluble and can leach out, leaving pores in the concrete.
Pozzolanic Reaction: Pozzolanic materials are siliceous materials that have no cementitious value on their own. However, in finely divided form and in the presence of moisture, they react chemically with the free Lime released during OPC hydration.
Result: This reaction converts the "useless" lime into additional, stable C-S-H (Calcium Silicate Hydrate) gel. This fills pores, increases long-term strength, and improves the impermeability and durability of the concrete.
Comparison: Pozzolanas do not react significantly with Gypsum or additional Silica. They specifically target the liberated Lime.
Step 3: Final Answer:
In PPC, the pozzolanic material reacts with the free Lime $(Ca(OH)_2)$ produced during cement hydration. Thus, option (B) is correct.