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