Explanation:

All of the above statements are correct. All the statements are correct.
• Fly ash is one of the coal combustion products, composed of the fine particles that are driven out of the boiler with the flue gases.
• Ash that falls in the bottom of the boiler is called bottom ash.
• In modern coal-fired power plants, fly ash is generally captured by electrostatic precipitators or other particle filtration equipment before the flue gases reach the chimneys. Together with bottom ash removed from the bottom of the boiler, it is known as coal ash.
• All fly ash includes substantial amounts of silicon dioxide (SiO2), aluminium oxide (Al2O3) and calcium oxide (CaO).
• Constituents of fly ash can be: Arsenic, beryllium, boron, cadmium, chromium, hexavalent chromium, cobalt, lead, manganese, mercury, molybdenum, selenium, strontium, thallium, and vanadium.
• In the past, fly ash was simply dispersed into the atmosphere. This created environmental and health concerns that prompted laws that have reduced fly ash emissions to less than 1% of ash produced.
• Worldwide, more than 65% of fly ash produced from coal power stations is disposed of in landfills and ash ponds.

Probable uses of fly ash:
1. Concrete production, as a substitute material for Portland cement and sand
2. Embankments and other structural fills (usually for road construction)
3. Ground and Flow able fill production
4. Waste stabilization and solidification
5. Cement clinkers production - (as a substitute material for clay)
6. Mine reclamation
7. Stabilization of soft soils
8. Road sub-base construction
9. As Aggregate substitute material (e.g. for brick production)
10. Mineral filler in asphaltic concrete
11. Agricultural uses: soil amendment, fertilizer, cattle feeders, soil stabilization in stock feed yards, and agricultural stakes
12. Loose application on rivers to melt ice
13. Loose application on roads and parking lots for ice control

EXP
Fly ash is a major particulate type of air pollutant affected the opening and closing of stomata by blocking the stomatal aperture and thereby allowed increased transpiration. Low dusting rate of fly ash increased chlorophyll contents significantly, while high dusting rate of fly ash reduced the chlorophyllase enzyme due to the alkalinity caused by excessive soluble salts on the leaf surface and also due to increase of foliar temperature which retarted chlorophylls or breakdown of chlorophyll to form pheophytin. Due to which photosynthesis in leaves also retarded. In present lower dose of fly ash dust was found beneficial for all plant growth (Length, fresh and dry weight of shoot and root and tillers no. leaf area); yield (Ear length, no. of grains/ear and weight of 100 grains) compared to control .While, both another doses (2.5 and 5.0 g m-2) caused reduction in all above parameters and reduction were higher in 5.0 g m-2 treatments. Similarly, all biochemicals (Photosynthetic pigments, seed protein and seed carbohydrates) were also increased at 1.25 g m-2 treated sets. Lower dose of fly ash was also found beneficial to all leaf epidermal characteristics (No. of adaxial and abaxial surface of stomata, length and width of stomatal aperture and no. and length of trichomes). All these parameters were increased significantly. After that there was gradual decrease in all these parameters at both doses (2.5 and 5.0 g m-2).
Fly-ash has great potentiality in agriculture due to its efficacy in modification of soil health and crop performance. The high concentration of elements (K, Na, Zn, Ca, Mg and Fe) in fly-ash increases the yield of many agricultural crops. But the use of fly-ash in agriculture is limited compare to other sector. An exhaustive review of numerous studies of last four decades took place in this study, which systematically covers the importance, scope and apprehension regarding utilization of fly-ash in agriculture. This study also identified some areas, like soil fertility and its response on cereal oil seed and vegetable crops. Agricultural lime application contributes to global warming as Intergovernmental Panel on Climate Change (IPCC) assumes that all the carbon in agricultural lime is finally released as CO2 to the atmosphere. It is expected that use of fly-ash instead of lime in agriculture can reduce net CO2 emission and also reduce global warming.