#include <bits/stdc++.h>
using namespace std;
const int maxN = 2e5 + 11;
const long long oo = 1e17 + 11;
int tcases = 1;
char ch;
int readInt() {
  bool fl = 0;
  while (ch = getchar(), ch != '-' && (ch < '0' || ch > '9'))
    ;
  if (ch == '-') {
    fl = 1;
    while (ch = getchar(), ch < '0' || ch > '9')
      ;
  }
  int r = ch - '0';
  while (ch = getchar(), ch >= '0' && ch <= '9') r = r * 10 + (ch - '0');
  return fl ? -r : r;
}
int N, M, K;
int A[maxN];
void testcase() {
  cin >> N;
  M = 2 * N;
  for (int i = 1; i <= M; ++i) cin >> A[i];
  sort(A + 1, A + 1 + M);
  int x = A[1], y = A[M];
  for (int i = 1; i <= N; ++i) x = max(x, A[i]);
  for (int i = 1; i <= N; ++i) y = min(y, A[i + N]);
  cout << y - x << endl;
  return;
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie();
  cout.tie();
  cin >> tcases;
  for (int i = 1; i <= tcases; ++i) testcase();
  return 0;
}
