Default (factory setting) Low Byte Fuse setting of ATmega328P is: 01100010; where the lower 3-bit has set the internal 8 MHz RC Oscillator. The CKDIV8 fuse bit is programmed by default; so, the operating frequency of the MCU is 1 MHz. The UART Section of the MCU can operate well at this frequency at Bd 9600 with 0.2% error which is same as that when the chip runs on 16 MHz external crystal at Bd 9600. Two chips of the same batch are working well and not the 3rd one -- is it possible that the internal RC oscillator of the 3rd one is way out due to manufacturing defect?