#include <bits/stdc++.h>
using namespace std;
long long int a[200020];
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  int t = 0, n = 0;
  cin >> t;
  while (t--) {
    cin >> n;
    for (int i = 1; i <= 2 * n; ++i) cin >> a[i];
    if (n == 1)
      cout << abs(a[2] - a[1]);
    else {
      sort(a + 1ll, a + 2ll * n + 1ll);
      cout << abs(a[n + 1] - a[n]);
    }
    cout << endl;
  }
}
