#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(false);
  int t;
  cin >> t;
  while (t--) {
    int n;
    cin >> n;
    int sze = n * 2;
    int arr[sze];
    for (int i = 0; i < sze; i++) cin >> arr[i];
    sort(arr, arr + sze);
    cout << arr[n] - arr[n - 1] << endl;
  }
  return 0;
}
