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