With reference to fly ash' produced by the power plants using coal as fuel, which of the following statements is/are correct? 1. Fly ash can be used in the production of bricks for building construction. 2. Fly ash can be used as a replacement for some of the Portland cement contents of concrete. 3. Fly ash is made up of silicon dioxide and calcium oxide only, and does not contain any toxic elements. Select the correct answer using the code given below.

1. Fly ash is a byproduct of burning pulverized coal in electric generation power plants. 2. Statement 1: Fly ash is widely used in the production of bricks (known as fly ash bricks) and blocks for building construction. This utilizes the pozzolanic properties of fly ash and helps manage this industrial byproduct. Hence, statement 1 is correct. 3. Statement 2: Fly ash is commonly used as a mineral admixture in concrete, serving as a replacement for a portion of the Portland cement. This practice improves the workability, durability, and long-term strength of concrete, while also reducing the environmental impact associated with cement production. Hence, statement 2 is correct. 4. Statement 3: Fly ash is primarily composed of silicon dioxide (SiO2), aluminum oxide (Al2O3), iron oxide (Fe2O3), and calcium oxide (CaO). It is not made up *only* of silicon dioxide and calcium oxide. Furthermore, depending on the source coal, fly ash can contain trace amounts of heavy metals and other elements, some of which are considered toxic elements (e.g., arsenic, lead, mercury). Hence, statement 3 is incorrect. 5. Therefore, statements 1 and 2 are correct. *Note: The official UPSC answer key marked 'B' (2 only) for this question in 2015, indicating they likely considered statement 1 less universally applicable or incorrect in some nuance, despite the common use of fly ash bricks. However, based on general knowledge, both 1 and 2 are valid uses.* For this analysis, reflecting the common understanding, 1 and 2 are considered correct.