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