#include <bits/stdc++.h>
using namespace std;
int main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  int T;
  cin >> T;
  while (T--) {
    int n;
    cin >> n;
    vector<int> a;
    a.resize(2 * n);
    for (int i = 0; i < 2 * n; ++i) {
      cin >> a[i];
    }
    sort(a.begin(), a.end());
    cout << a[n] - a[n - 1] << '\n';
  }
  return 0;
}
