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