Step 1: Statement (I)
Absolute (potential) natality is the greatest number of births possible under ideal conditions. Realised natality is the actual birth rate, which is limited by real conditions. So absolute natality is larger and Statement (I) is correct.
Step 2: Statement (II)
Absolute (minimum) mortality is the death rate under ideal conditions, when individuals die only of old age. Realised mortality includes deaths from predators, disease and food shortage, so it is larger. Statement (II) is incorrect.
Step 3: Conclusion
Statement (I) is correct but Statement (II) is incorrect.
Final Answer:
Statement (I) is correct and Statement (II) is incorrect.
\[ \boxed{\text{(C) }\text{Statement (I) is correct but Statement (II) is incorrect.}} \]