#include <bits/stdc++.h>
using namespace std;
void solve() {
  int n, a[200005];
  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] << '\n';
  return;
}
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  int t;
  cin >> t;
  while (t--) {
    solve();
  }
  return 0;
}
