This is one of the Impatiens, called Bizzie Lizzie in the UK and though these are easy to care for, we don't get the heat that presumably you get in India!
One of the sites I was looking at has the following:

"Impatiens flower best when protected from the heat and intensity of direct sun. Plant them in partially shaded beds, such as those that receive bright, filtered light beneath trees. Beds exposed to two to four hours of morning sun but shaded from afternoon sun also work well. Too much sun and heat dries the soil too quickly and causes the foliage to lose moisture through rapid evaporation, resulting in wilted, dying plants and poor flowering."

So perhaps yours is in direct sunlight and getting too much heat. They do grow fine in pots, so don't need to be in the ground.

There are lots of cultivars of these, but yours could be this one.

https://en.wikipedia.org/wiki/Impatiens_walleriana

They do root easily just by putting a cutting in water until it has some roots, so perhaps you could try that as well.

More sensible advice from someone with more knowledge, will probably be forthcoming.

This is not the usual Bizzie Lizzie. It's Impatiens 'New Guinea', which does not like sun at all. Keep it permanently-shaded and well-watered (the compost should be moist at all times), and deadhead it regularly to ensure a succession of blooms.