#include <bits/stdc++.h>
using namespace std;
const int N = 200005;
int n;
int A[N];
int main() {
  int t;
  scanf("%d", &t);
  while (t--) {
    scanf("%d", &n);
    n *= 2;
    for (int i = 1; i <= n; i++) {
      scanf("%d", &A[i]);
    }
    sort(A + 1, A + 1 + n);
    n /= 2;
    printf("%d\n", A[n + 1] - A[n]);
  }
  return 0;
}
