what ll happen if i provide clk to 89v51rd2 using function generator (square wave of 10MHz) instead of using crystal oscillator ?

 

The processor does not care. Off course all of the other connections must be correct and there must be a program for it to execute. If the code memory is erased to all zeros or all ones you might want to figure out what instruction that is that will be executed repeatedly.

RTFDS and look for a section called "External Clock"

 

When driving the device from an external clock source, XTAL2 should be left disconnected and XTAL1 should be driven. The data sheet has section about this.​