Transistors

it's (a)
I_CBO = I_c - βI_B
= (51.2 - 125 x 0.39) mA
= 2.45 mA

hence the answer [1]

Thank you,can you please give me any link on info about transistors?I am not form CBSE syll.

me too not CBSE and i'm state board but i have electronics as my fourth optional in my college so was able to do that question.........
between if u want link may be u shuld try google it...
I don't have any such link[1]

http://www.notemonk.com/book/23/Physics%202%20Class%2012/

You can download the NCERT text book from the above link

Detailed info about semi conductors, transistors is given.