#include <bits/stdc++.h>
using namespace std;
int a[200010];
int main() {
  int T;
  cin >> T;
  while (T--) {
    int n;
    cin >> n;
    for (int i = 1; i <= n * 2; i++) cin >> a[i];
    sort(a + 1, a + 1 + n * 2);
    printf("%d\n", a[n + 1] - a[n]);
  }
}
