#include <bits/stdc++.h>
using namespace std;
long long arr[200005] = {0};
int main() {
  long long cases, size;
  long long xh;
  cin >> cases;
  while (cases--) {
    cin >> size;
    for (xh = 0; xh < 2 * size; xh++) {
      cin >> arr[xh];
    }
    sort(arr, arr + 2 * size);
    cout << arr[size] - arr[size - 1] << endl;
  }
  return 0;
}
