Correct answer: (a) 1 and 2
Explanation
- 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.
- B
2 only
(b) 2 only. Cement replacement is correct, but brick use is also established. 2 only is too narrow.
- C
1 and 3
(c) 1 and 3. Bricks are valid; the ‘only SiO2 and CaO, no toxics’ claim is not. The pair fails.
- 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.
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