NIT

157 some how may not be good enough for general category and without state quota. I still think that depends upon the competition and interest of people above you. but even if you don't get in to mechanical NITK, don't loose your hope. There are plenty of other colleges like NIT Allahabad or Rourekela that you can get into and build an outstanding career. Even though NITK looks a tough nut, all the best for your future endeavors.

no chance brother

Getting admissions in these institutions is little difficult as their cut-off is little high but you may get admission in premier private institutions which along with good education provides a platform from where their students can sharp their skills and can achieve excellence.here are some of the colleges where you may get admission:
1.BITS
2.Lovely Professional university
3.VIT
you can apply for their entrance examination and can avail scholarship.Lovely Professional University venture in their students an unmatched entrepreneurial skills that make their students an efficient managers.

minimum 190 for sc category

You can get metallurgical in mnit jaipur, mining engineering at vnit nagpur, biotechnology or ceramic engineering at nit rourkela etc.

I dont really have an idea about the civil branch but I think you can get it at some nit as the cutoff for civil is quite low as compared to cse. Although nit delhi does not offer civil as one of its courses in my opinion.

Which category he belongs to?

You might get NIT under state quota.

All are good. But, if set in an order:
1) BITS
2) NIT
3) VIT
4) IIIT