#include <bits/stdc++.h>
using namespace std;
const int N = 2e5 + 5, M = 1e6 + 6, OO = 0x3f3f3f3f;
int n, arr[N];
int tc;
int main() {
  cin >> tc;
  while (tc--) {
    cin >> n;
    for (int i = 0; i < 2 * n; i++) cin >> arr[i];
    sort(arr, arr + 2 * n);
    cout << abs(arr[n] - arr[(n - 1)]) << endl;
  }
  return 0;
}
