Q.Tomato flower rot
My tomato flowers bloom then the stem rots and fall off.

There can be several reasons for blossom drop on plants, including temperature fluctuations, watering issues, insects, disease, pollination, and nitrogen levels to high.
Here are some links to help you.
https://www.gardeningknowhow.com/edible/vegetables/tomato/growing-temp-for-tomatoes.htm
https://www.gardeningknowhow.com/plant-problems/environmental/why-healthy-blooms-fall.htm
https://www.gardeningknowhow.com/edible/vegetables/tomato/tomato-diseases.htm
https://www.gardeningknowhow.com/edible/vegetables/tomato/growing-tomatoes-guide.htm