#include <bits/stdc++.h>
using namespace std;
int main() {
  int t;
  scanf("%d", &t);
  for (int i = 1; i <= t; i++) {
    int n;
    scanf("%d", &n);
    int x = 2 * n;
    int a[x + 1];
    for (int i = 0; i < x; i++) scanf("%d", &a[i]);
    sort(a, a + x);
    cout << a[n] - a[n - 1] << endl;
  }
}
