#include <bits/stdc++.h>
using namespace std;
const unsigned int M = 1000000007;
void solve() {
  int n;
  cin >> n;
  ;
  int arr[2 * n];
  for (int i = 0; i < 2 * n; i++) cin >> arr[i];
  sort(arr, arr + 2 * n);
  cout << arr[n] - arr[n - 1] << endl;
}
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  int t;
  cin >> t;
  ;
  while (t--) solve();
}
