The correct answer is: None of the above.
The formula for memory capacity is $MC = 2^N$, where $N$ is the number of bits. This formula is based on the fact that each bit can store one of two values, 0 or 1. Therefore, the number of possible combinations of bits is $2^N$.
Option A is incorrect because it divides the number of bits by 2. This would reduce the amount of memory available.
Option B is incorrect because it divides the number of bits by 2. This would reduce the amount of memory available.
Option C is incorrect because it squares the number of bits. This would increase the amount of memory available, but it is not the correct formula.
Option D is incorrect because it raises 2 to the power of $N$. This is the correct formula for memory capacity, but it is not one of the options.