#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  int arr[200001], n, x, ans = 0;
  long long int t;
  cin >> t;
  while (t--) {
    cin >> n;
    for (int i = 0; i < 2 * n; i++) cin >> arr[i];
    sort(arr, arr + 2 * n);
    int a = 0, b = 0;
    cout << abs(arr[n] - arr[n - 1]) << "\n";
  }
  return (0);
}
