#include <bits/stdc++.h>
using namespace std;
int a[200005];
int read() {
  int A;
  bool K;
  char C;
  C = A = K = 0;
  while (C < '0' || C > '9') K |= C == '-', C = getchar();
  while (C > '/' && C < ':') A = (A << 3) + (A << 1) + (C ^ 48), C = getchar();
  return (K ? -A : A);
}
int main() {
  int t, n, i;
  t = read();
  while (t--) {
    n = read();
    for (i = 1; i <= n << 1; i++) a[i] = read();
    sort(a + 1, a + (n << 1 | 1));
    printf("%d\n", a[n + 1] - a[n]);
  }
  return 0;
}
