#include <bits/stdc++.h>
using namespace std;
int pre[200005];
int main() {
  int t, n;
  cin >> t;
  while (t--) {
    cin >> n;
    n <<= 1;
    for (int i = 0; i < n; ++i) cin >> pre[i];
    sort(pre, pre + n);
    cout << pre[n / 2] - pre[n / 2 - 1] << endl;
  }
  return 0;
}
