An optimizer compiler is a type of compiler that aims to improve the efficiency and performance of the generated code. It does this by analyzing the source code and applying various optimization techniques to produce optimized machine code. However, in this case, the correct answer is option 'D' - None of the mentioned.

Explanation:
1. Optimize the code:
- One of the primary tasks of an optimizer compiler is to optimize the code. It achieves this by applying various optimization techniques such as loop unrolling, constant propagation, dead code elimination, and many more.
- These optimization techniques aim to improve the runtime efficiency of the code, reducing unnecessary computations, and improving overall performance.

2. Is optimized to occupy less space:
- The second option states that an optimizer compiler is optimized to occupy less space. This implies that the compiler is designed to generate code that takes up less memory or storage.
- While it is true that some optimization techniques can reduce the size of the generated code, it is not the primary goal of an optimizer compiler. The main focus is on improving performance rather than reducing code size.

3. Both of the mentioned:
- The third option suggests that both optimizing the code and occupying less space are correct regarding an optimizer compiler. However, as discussed earlier, reducing code size is not the primary goal of an optimizer compiler.
- While some optimizations may result in smaller code, it is not a guaranteed outcome of an optimizer compiler.

4. None of the mentioned:
- The correct answer is 'None of the mentioned' because neither option a) nor option b) accurately describes the primary purpose of an optimizer compiler.
- An optimizer compiler is primarily focused on improving the performance and efficiency of the generated code by applying various optimization techniques.
- The goal is to make the code faster and more efficient, not necessarily to reduce its size.

In conclusion, the correct answer is option 'D' - None of the mentioned because neither option a) nor option b) accurately describes the primary purpose of an optimizer compiler. The primary goal of an optimizer compiler is to improve the performance and efficiency of the generated code, rather than simply optimizing the code or reducing its size.