#include <bits/stdc++.h>
using namespace std;
void solve() {
  int n;
  cin >> n;
  n *= 2;
  vector<int> a(n);
  for (int i = 0; i < n; i++) cin >> a[i];
  sort(a.begin(), a.end());
  cout << a[n / 2] - a[n / 2 - 1] << endl;
}
int main() {
  int t;
  cin >> t;
  while (t--) {
    solve();
  }
}
