#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  int t, n, arr[(int)2e5 + 5];
  cin >> t;
  while (t--) {
    cin >> n;
    for (int i = 0; i < 2 * n; i++) cin >> arr[i];
    sort(arr, arr + (2 * n));
    cout << abs(arr[n - 1] - arr[n]) << endl;
  }
  return 0;
}
