#include <bits/stdc++.h>
using namespace std;
int32_t main() {
  long long t;
  cin >> t;
  while (t--) {
    long long n;
    cin >> n;
    long long total = 2 * n;
    vector<long long> a(total);
    for (long long i = 0; i < total; ++i) {
      cin >> a[i];
    }
    sort(a.begin(), a.end());
    cout << a[n] - a[n - 1] << endl;
  }
  return 0;
}
