Answer: (ii) The amount of physical memory used

Explanation:

• Space complexity is the total amount of memory (in terms of asymptotic function of input size $n$) required by an algorithm to run to completion, including:

  • Input space / auxiliary space for variables, data structures, recursion stack, dynamically allocated memory.
  • Often reported as auxiliary space (extra space excluding input itself).

• (i) number of input elements is $n$ itself, not space complexity.

• (iii) number of recursive calls contributes to stack space but is only one component.

• (iv) lines of code is program size / software metric, unrelated to asymptotic memory usage.

Hence space complexity = memory consumed as function of $n$, e.g., iterative linear search $O(1)$, merge sort $O(n)$, recursive DFS $O(h)$ stack.

Correct choice: (ii)