I want to connect RGB led to the output of the LM741 op amp.Do I need to use BJT ? If I don't .Can op-amp provide enough current to RGB? Secondly ,Can I connect 3 pin of the RGB to the output without buffer?
That depends on how bright you want them.
An LM741 is only good for 25mA MAX before it goes into current limit. So if you are planning on driving those LEDs with more than about 8mA each, then no the poor old 741 can't drive them that hard.
Driving the 741 at +-12V will also put too high a reverse voltage on the LEDs at around -10V output. You would need to add a diode to protect the LEDs.
Ultimately you would be better adding an NPN Transistor or a suitable MOSFET.
The diode D2 in the above protects the base-emitter junction of the NPN from breaking down when the op-amp output is negative.
BTW, if you just want a white LED you would be better with a single white LED, and the 741 is very old technology. Although Op-Amps can be used as comparators like that, they are not great at the role, a suitable actual comparator, with sufficient drive, would be a better choice all round.
No you should not. What you should do is consider what output you need for function, current and choose logic level drivers with R’s using Ohm’s Law and correct diode orientation. (That is 3 strikes or bad assumptions in your question) Also Comparator are different from OA’s with more low state drive current as in open collector.
For more ideas search “Light Organ”