#include <bits/stdc++.h>
using namespace std;
const int N = 3e5 + 20;
int a[N];
void solve() {
  int n;
  cin >> n;
  for (int i = 1; i <= 2 * n; i++) {
    cin >> a[i];
  }
  sort(a + 1, a + 2 * n + 1);
  cout << a[n + 1] - a[n] << endl;
}
int main() {
  int t;
  cin >> t;
  while (t--) {
    solve();
  }
}
