With reference to ‘fly ash’ produced by the power plants using the 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 codes given below:

Statements 1 and 2 are correct, and statement 3 is wrong, so the answer is A.

• Statement 1 is correct. Fly ash is a pozzolanic material, so it is used to make fly ash bricks, which are lighter and save topsoil compared with clay bricks. Government notifications since 2016 have pushed its use in construction.
• Statement 2 is correct. Fly ash replaces part of the Portland cement in concrete and in Portland Pozzolana Cement (PPC). It improves long-term strength, workability and durability.
• Statement 3 is wrong. Fly ash is mainly silica, alumina and iron oxide, with some lime. It also contains trace toxic elements such as arsenic, lead, mercury, cadmium and chromium, which is why its disposal and handling are regulated.

The core concept is pozzolanic activity and the waste-to-resource idea. It links to Mains GS III on environment, pollution control and sustainable construction, and to the push for green building materials.

Trap: Students see "silicon dioxide and calcium oxide" and assume the ash is harmless. Fly ash does contain toxic trace elements, so statement 3 is false.