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.

Statements 1 and 2 are correct because fly ash possesses pozzolanic properties, making it an effective raw material for manufacturing lightweight bricks and a sustainable partial replacement for Portland cement in concrete. Statement 3 is the most tempting error but is incorrect because fly ash contains toxic heavy metals—such as arsenic, lead, and mercury—and its chemical composition includes aluminum and iron oxides in addition to silicon and calcium. The core concept tested is the sustainable utilization of industrial waste (resource recovery) and the environmental hazards associated with coal combustion by-products.