#include <bits/stdc++.h>
using namespace std;
const int N = 200100;
int main() {
  ios_base::sync_with_stdio(false);
  int t;
  cin >> t;
  while (t--) {
    int n;
    cin >> n;
    int a[n << 1];
    for (int i = 0; i < n << 1; ++i) {
      cin >> a[i];
    }
    sort(a, a + (n << 1));
    n <<= 1;
    int ans = 1e9 + 1;
    for (int i = 0; i < n; ++i) {
      if (i == n - i - 2) {
        ans = a[i + 1] - a[i];
      }
    }
    cout << ans << '\n';
  }
  return 0;
}
