#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  long long n, k, m, t;
  cin >> t;
  while (t--) {
    cin >> n;
    long long a[2 * n + 5];
    for (long long i = 1; i <= n * 2; i++) cin >> a[i];
    sort(a + 1, a + 2 * n + 1);
    cout << a[n + 1] - a[n] << endl;
  }
  return 0;
}
