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