#include <bits/stdc++.h>
using namespace std;
template <class T>
inline void out(T t) {
  cout << t << "\n";
}
template <class T, class... Ts>
inline void out(T t, Ts... ts) {
  cout << t << " ";
  out(ts...);
}
template <class T>
inline bool CHMAX(T& a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <class T>
inline bool CHMIN(T& a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
constexpr long long INF = 1e9;
void solve() {
  long long N;
  cin >> N;
  vector<long long> a(N * 2);
  for (long long i = 0; i < (long long)(N * 2); i++) {
    cin >> a[i];
  }
  sort(a.begin(), a.end());
  out(a[N] - a[N - 1]);
}
signed main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  long long Q = 1;
  cin >> Q;
  while (Q--) solve();
}
