Q.fertilizer for marigold plants
Chemical fertilizer…if organic, then how to prepare it?

golds: fertilizer is not so important for these plants as for some others. Use a balanced fertilizer (1:1:1 or 3:1:2 proportions) once in the early spring. Learn more about marigolds here: https://www.gardeningknowhow.com/ornamental/flowers/marigold/growing-marigold-flowers.htm
You can use a commercial fertilizer, or organic fertilizer. If you want to go organic, the best thing is to work compost (decomposed organic matter) into the soil before planting. Learn more about fertilizer here: https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/fertilizer-numbers-npk.htm
organic fertilizer: https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/homemade-plant-food.htm
and compost: https://www.gardeningknowhow.com/composting/