#include <bits/stdc++.h>
using namespace std;
const int maxn = 2 * 1e5 + 10;
int main() {
  int T;
  cin >> T;
  int n;
  int a[maxn];
  while (T--) {
    cin >> n;
    for (int i = 0; i < 2 * n; i++) cin >> a[i];
    sort(a, a + 2 * n);
    cout << a[n] - a[n - 1] << endl;
  }
}
