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