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 can be used in the production of bricks for building construction: This statement is correct. Fly ash is a common pozzolanic material used to produce fly ash bricks, which are an eco-friendly and often more durable alternative to traditional clay bricks. It helps conserve topsoil and reduces the amount of waste sent to landfills. 2. Fly ash can be used as a replacement for some of the Portland cement contents of concrete: This statement is correct. Fly ash, due to its pozzolanic properties, reacts with the calcium hydroxide in cement hydration to form cementitious compounds. It is widely used as a supplementary cementitious material (SCM) in concrete, improving its strength, durability, and workability, while reducing cement consumption and carbon emissions. 3. Fly ash is made up of silicon dioxide and calcium oxide only, and does not contain any toxic elements: This statement is incorrect. While fly ash is primarily composed of silicon dioxide (SiO2), aluminium oxide (Al2O3), iron oxide (Fe2O3), and calcium oxide (CaO), its composition varies depending on the type of coal burned. Crucially, it often contains various trace elements, some of which can be toxic, such as arsenic, lead, mercury, chromium, and cadmium. Therefore, it is not composed 'only' of silicon dioxide and calcium oxide, and it 'does' contain toxic elements, necessitating careful management and disposal.