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