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