Can I get Admission to 2nd year B.Sc after diploma??? Is there any entrance examination for this???

Yes, you can get Admission to 2nd year B.Sc after diploma, for the admission you need to appear in the B.Sc lateral entry test.

There are number of colleges who would give admission in B.Sc lateral entry to the diploma holders. The requirements vary from college to college.

You can also take admission in the 2nd year of the engineering course after completing B. Sc. and I would suggest you to get admission in this program rather then B. sc. for your reference here I am giving you the list of most reputed science colleges:

Shri Ram College of Commerce,Delhi.
St.Xavier's College,Mumbai.
Loyola College, Chennai.
St. Xavier’s College, Kolkata.
St.Joseph’s College, Banglore.
LSR College for Women, Delhi.
Presidency College, Chennai.
BM College, Pune.
Christ College, Bangalore.
Hindu College, Delhi.
Indian Institute of Management & Commerce, Hyderabad.
HL College of Commerce, Ahmedabad.
Hans Raj College, Delhi.
Jesus & Mary College,Delhi.
RA Poddar College, Mumbai.