#include <bits/stdc++.h>
using namespace std;
void solve() {
  int n;
  cin >> n;
  vector<int> arr(2 * n);
  for (auto &x : arr) cin >> x;
  sort(arr.begin(), arr.end());
  int ans = 0;
  cout << arr[n] - arr[n - 1] << '\n';
}
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  int t;
  cin >> t;
  while (t--) solve();
  return 0;
}
