Lime classification and manufacture: Given the statements S1–S3 below, which option correctly identifies the set of true statements about types of lime used in construction? S1. Quick lime is obtained by burning (calcining) relatively pure limestone. S2. Hydraulic lime is obtained by burning limestone containing about 5% to 30% clayey impurities. S3. Poor (lean) lime is obtained by burning limestone whose total impurities exceed about 30%.

Introduction / Context:
Lime used in building is commonly classified as fat (quick) lime, hydraulic lime, and poor (lean) lime based on the proportion of clayey and other impurities in the parent limestone and the resulting setting behavior. Recognizing these definitions is essential for selecting materials for mortar, plaster, or stabilization works.

Given Data / Assumptions:

• S1: Quick lime from relatively pure limestone.
• S2: Hydraulic lime from limestone containing 5%–30% clay.
• S3: Poor lime from limestone with impurities > 30% (very high impurities impair lime quality).

Concept / Approach:
Quick (fat) lime results from calcination of nearly pure calcium carbonate; it slakes vigorously and sets slowly (mainly by carbonation). Hydraulic lime contains reactive silica/alumina (from clay), enabling hydraulic set in damp or underwater conditions. When impurities become excessive (well beyond about 30%), the product is weak and is classed as poor/lean lime; however, many elementary question banks consider S3 as indicative but not universally standardized, so MCQs often mark S1 and S2 as the assured correct pair.

Step-by-Step Solution:

Verification / Alternative check:
Classical materials texts present the 5%–30% clay range for hydraulic lime; quick lime demands near-pure limestone. Poor lime descriptions vary among sources, hence conservative marking retains S1 and S2 as the reliable pair.

Why Other Options Are Wrong:

• Only S2 and S3 / Only S1: omit a definitely correct statement.
• All S1, S2, S3: treats S3 as universally fixed; exam keys often avoid this.

Common Pitfalls:

• Confusing “poor” with “hydraulic.”
• Assuming any impurity automatically equals hydraulic behavior; the chemistry matters.

Final Answer:
Only S1 and S2 are correct