#include <bits/stdc++.h>
using namespace std;
int main() {
  ios::sync_with_stdio(false);
  int i, j, t, n, a;
  cin >> t;
  while (t--) {
    int k, b;
    priority_queue<int> q;
    cin >> n;
    for (i = 1; i <= 2 * n; i++) {
      cin >> a;
      q.push(a);
    }
    k = n - 1;
    while (k--) {
      q.pop();
    }
    a = q.top();
    q.pop();
    b = q.top();
    cout << a - b << '\n';
  }
}
