Hi Ajay,
Coming to your question the exams after your 12 for a govt job I should think is NDA as it is held twice a year ,by this you will get commissioned in the defence as an officer I am telling the exams only for the officers entry in govt job
You can also apply for army tes entry if you have 70% above in your boards. These all are the officers entry.

And competitive exam that you should go for to get a good college is wbjee, jee mains, bitsat by this exam you will get a good college and the reputed one to.
Hope this help you if you still have doubt fell free to ask