#include <bits/stdc++.h>
using namespace std;
int main() {
  long long t;
  cin >> t;
  for (long long i = 0; i < t; i++) {
    long long n;
    cin >> n;
    long long a[(2 * n)];
    for (long long u = 0; u < (2 * n); u++) cin >> a[u];
    sort(a, a + (2 * n));
    cout << abs(a[n] - a[n - 1]) << endl;
  }
}
