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