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There are white soft salt like crystals formed in the soil of my basil plant. i want to know all about these white soil crystals and how to remove them

If your humidity is really low indoors, then I could suggest this, but doing this without proper ventilation will result in rot and, ultimately, the death of the plant.

You can spray the plant once or twice per day to increase the humidity of the area around it. You will also want to give this plant as much light as possible. If you do not have a South facing Window, then you will need a horticultural light to help supplement.

Here is an article for more information: https://www.gardeningknowhow.com/edible/herbs/basil/information-on-how-to-grow-basil-indoors.htm

There should be now lowering of quality as long as you harvest from healthy plants and store seed properly.
Here is a link with more information.

https://www.gardeningknowhow.com/edible/herbs/basil/harvesting-basil-seeds.htm

I would treat the soil for a fungal infection. You can do this by replacing 1/4 of your water with peroxide when watering. This will kill off anything lurking in the soil, as well as give extra oxygen to the roots.

Make sure that you only water when the top of the soil is almost completely dry. Basil can be moderately drought tolerant, but will quickly get an infection if left too wet for too long.

They won't get scorched where you have them. They are tolerant of full sun, so they may get pretty stretchy only getting eastern sun. South facing would be ideal. If you need, you may even want to get supplemental lighting. This will help you to get a little more light to them. I have grown them under 750 watts of insanely powerful LED's and they respond very well.

I would not spray them for moisture. They are actually slightly drought tolerant. Spraying them will make them susceptible to powdery mildew infections.

This article will give you more information: https://www.gardeningknowhow.com/edible/herbs/basil/information-on-how-to-grow-basil-indoors.htm

In VERY VERY small amounts, and used correctly as an insecticide and antifungal, it won't hurt them. If you add it to water into the soil as nutrients then it will have a devastating cascade of effects leading to the death of the plant. Baking soda has to be used correctly when it comes to gardening, as the sodium that it contains is way too much for most plants to be able to handle.