#include <bits/stdc++.h>
using namespace std;
const int N = 500;
int n;
int main() {
  std ::ios ::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  int t;
  cin >> t;
  for (; t--;) {
    cin >> n;
    vector<int> vt(n << 1);
    for (int &i : vt) {
      cin >> i;
    }
    sort(vt.begin(), vt.end());
    cout << vt[n] - vt[n - 1] << endl;
  }
  return 0;
}
