Hello Manju,
Yes, you can write KCET exam but it is not necessary for B.Sc in Electronics and Communication. Only those candidates who are interested in courses like horticulture/Agriculture/Forestry/Sericulture/Biotechnology/community science they should appear for KCET Exam except them all other courses in B.Sc can be taken by the candidates without appearing for KCET Exam.
I suggest you to write KCET Exam because you'll write the exam once in your life you shouldn't miss it, tomorrow you shouldn't regret yourself by saying that if I would have written KCET there might be a chance to get a better course than Electronics and Communication.
If you have choosen by your interest it is well and good otherwise, you should prefer to write KCET.
Hope I have answered your question in an easy way.
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