#include <bits/stdc++.h>
using namespace std;
void SADIEM() {
  std::ios_base::sync_with_stdio(NULL);
  cin.tie(0);
  cout.tie(0);
}
int main() {
  SADIEM();
  int t;
  cin >> t;
  while (t--) {
    int n;
    cin >> n;
    vector<int> v(2 * n);
    for (int i = 0; i < 2 * n; i++) cin >> v[i];
    sort(v.begin(), v.end());
    cout << v[n] - v[n - 1];
    if (t) cout << "\n";
  }
}
