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