Correct Answer: 345

Solution : First option: 679; 6 and 7 are consecutive numbers and are written at hundreds place digit and tens place digit respectively, while the units place digit is 9, which is 2 more than the tens place digit.

Second option: 124; 1 and 2 are consecutive numbers and are written at hundreds place digit and tens place digit respectively, while units place digit is 4, which is 2 more than the tens place digit.

Third option: 568; 5 and 6 are consecutive numbers and are written at hundreds place digit and tens place digit respectively, while units place digit is 8, which is 2 more than the tens place digit.

Fourth option: 345; 3 , 4 and 5 are consecutive numbers and are written at hundreds place digit, tens place digit and units place digit respectively.

Therefore, 345 is different from the other three.

Hence, fourth option is correct.