#include <bits/stdc++.h>
using namespace std;
int main() {
  int t;
  int n;
  cin >> t;
  for (int i = 0; i < t; i++) {
    cin >> n;
    int arr[2 * n];
    for (int j = 0; j < 2 * n; j++) {
      cin >> arr[j];
    }
    sort(arr, arr + 2 * n);
    vector<int> left, right;
    for (int j = 0; j < 2 * n; j++) {
      if (j == 2 * n - 1) {
        if (n % 2 == 0) {
          if (j % 2 != 0)
            left.push_back(arr[j]);
          else
            right.push_back(arr[j]);
        } else {
          if (j % 2 == 0)
            left.push_back(arr[j]);
          else
            right.push_back(arr[j]);
        }
      } else {
        if (j % 2 == 0)
          left.push_back(arr[j]);
        else
          right.push_back(arr[j]);
      }
    }
    cout << abs(left[left.size() / 2] - right[right.size() / 2]) << "\n";
  }
  return 0;
}
