#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  for (int x = 0; x < n; x++) {
    int m;
    cin >> m;
    int arr[m * 2];
    for (int x = 0; x < m * 2; x++) {
      cin >> arr[x];
    }
    sort(arr, arr + m * 2);
    cout << arr[m * 2 / 2] - arr[m * 2 / 2 - 1] << endl;
  }
}
