Question: nRF51 SOC does the SOC support I2C SLAVE Interface?

 
Answer: The nRF51x22 does not have a I2C Slave interface. The nRF52832 has I2C Slave (called TWIS in the datasheet) and there is an example showing this in the nRF5 SDK v11: nRF5_SDK_11.0.0_89a8197\examples\peripheral\twi_master_with_twis_slave