#include <bits/stdc++.h>
using namespace std;
vector<int> a;
int main(int argc, char const *argv[]) {
  int t;
  cin >> t;
  for (int i = 0; i < t; ++i) {
    a.clear();
    int n;
    cin >> n;
    for (int j = 0; j < 2 * n; ++j) {
      int x;
      cin >> x;
      a.push_back(x);
    }
    sort(a.begin(), a.end());
    printf("%d\n", a[n] - a[n - 1]);
  }
  return 0;
}
