#include <bits/stdc++.h>
using namespace std;
int t, n, a[200000];
int main() {
  scanf("%d", &t);
  while (t--) {
    scanf("%d", &n);
    for (int i = 0; i < 2 * n; i++) scanf("%d", a + i);
    sort(a, a + 2 * n);
    printf("%d\n", abs(a[n - 1] - a[n]));
  }
  return 0;
}
