#include <bits/stdc++.h>
using namespace std;
const double pi = acos(-1.0);
const int N = 1e5;
int main() {
  ios::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  int tc, ca = 0;
  cin >> tc;
  while (tc--) {
    int n, el;
    vector<int> v;
    cin >> n;
    for (int i = 0; i < n + n; i++) {
      cin >> el;
      v.push_back(el);
    }
    sort(v.begin(), v.end());
    cout << v[n] - v[n - 1] << '\n';
  }
  return 0;
}
