how to set default I2C pin(SDA AND SCL) for nrf52832 using UICR customer register?

[dewal]

How to set  SDA= p0.25;and SCL=P0.26 default pin configration.

[dewal]

#define TWI0_CONFIG_FREQUENCY    NRF_TWI_FREQ_100K
#define TWI0_CONFIG_SCL 0x1b
#define TWI0_CONFIG_SDA 0x1a

Is this PSEL_xx register configuration?? 

0x1b and 0x1a  are bit selection in  PSEL.SCA and PSEL.SDA  ???

if  these are correct, then tell me how they get write this exact vslues on the register?

[Turbo J]

The PS (V1.4, chapter 49.8.6) leaves no ambiguity here:

"PSELSCL [0..31] Pin number configuration for TWI SCL signal".

Any experienced programmer can calculate the decimal pin number from those simple hex values - and everybody else just uses windows calculator in programmer mode.

SCL is  P0.26, SDA is P0.27 as shown here.

Dunno why the values are encoded in hex in your case. Decimal values work fine here, and would match the P0.xx values from the PS.