What is the worst case time complexity of inserting $n$ elements into an empty linked list, if the linked list needs to be maintained in sorted order?

To maintain a singly linked list in sorted order while inserting $n$ elements one by one:

1. Inserting the $1^{\text{st}}$ element takes $O(1)$ operations.

2. In the worst case, inserting the $k^{\text{th}}$ element requires traversing all $k-1$ previously inserted elements to find the correct insertion position, taking $\Theta(k-1)$ comparisons and pointer updates.

3. The total worst-case time across all $n$ insertions is:

   $$\sum_{k=1}^{n} \Theta(k-1) = \Theta\left(\frac{n(n-1)}{2}\right) = \Theta(n^2)$$

Hence, the worst-case time complexity is $\Theta(n^2)$, which corresponds to option C.