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 codes given below

1. A

   1 and 2

   (a) 1 and 2. Fly ash is widely used in bricks and as a partial replacement for Portland cement in concrete (pozzolana). Statement 3 is false: fly ash is not only SiO2 and CaO and can carry toxic traces (arsenic, mercury, lead). 1 and 2 is the official key.

2. B

   2 only

   (b) 2 only. Cement replacement is correct, but brick use is also established. 2 only is too narrow.

3. C

   1 and 3

   (c) 1 and 3. Bricks are valid; the ‘only SiO2 and CaO, no toxics’ claim is not. The pair fails.

4. D

   3 only

   (d) 3 only. Statement 3 is the incorrect one, so it cannot be the key.

Summary. Official key is (a) 1 and 2. Coal fly ash goes into bricks and can replace part of Portland cement. It is a mixed oxide ash and may contain toxic elements, so statement 3 is wrong. The keyed choice is bricks plus cement replacement.