#include <bits/stdc++.h>
const int mod = 1e9 + 7;
const int mx = 1e5 + 5;
using namespace std;
int solve() {
  int n;
  cin >> n;
  n *= 2;
  int arr[n];
  for (int i = 0; i < n; i++) cin >> arr[i];
  sort(arr, arr + n);
  cout << arr[n / 2] - arr[n / 2 - 1] << endl;
  return 0;
}
int main() {
  ios_base::sync_with_stdio(false), cin.tie(0), cout.tie(0);
  int q;
  cin >> q;
  while (q--) solve();
}
