Uses for Transistor?

ok sceadwian i do agree with you but tell me one thing you can use the transistor for switching as well as for the amplification but you can not go beyond its frequency range...??? correct me if i am wrong please.

Depends rahul. Manufactoring tollerances can lead to VERY wide frequency ranges, so you will find chips which perform outside their datasheets.
Generally speaking however you are correct, however it depends HIGHLY on the SPECIFIC use, as suitability for a low distortion or high distortion amplifier will lead to extremely different transistor choices.

thanks sceadwian.