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