We've shown that you can represent a binary tree using an array. Would it be good to implement Red$-$Black trees as an array?

It's difficult to say, because even with a Red$-$Black tree, the tradeoff between wasted space $($due to unused array elements$)$ and space savings $($due to the absence of pointers$)$ depends on the specifics of the actual tree.

No$,$ because each rotation would cause a large amount of data movement, killing performance gains.

Yes, because an array representation obviates the need for both child pointers and expensive parent pointers.

Yes, because we know that the tree has $O(logn)$ height, so the amount of unused array elements would be limited$.$

No$,$ because it would be difficult to recolor array elements red and black.