#include <bits/stdc++.h>
using namespace std;
int main() {
  int t;
  cin >> t;
  while (t--) {
    int n;
    cin >> n;
    long a[n * 2], sum = 0;
    for (int i = 0; i < n * 2; i++) {
      cin >> a[i];
    }
    sort(a, a + (n * 2));
    int m = n;
    cout << abs(a[m] - a[m - 1]) << endl;
  }
  return 0;
}
