#include <bits/stdc++.h>
using namespace std;
const int MOD = (int)1e9 + 7;
int t;
void solve() {
  long long n;
  cin >> n;
  vector<long long> a(n * 2);
  for (auto &i : a) cin >> i;
  sort(a.begin(), a.end());
  cout << a[n] - a[n - 1] << endl;
}
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  if (1) {
    cin >> t;
    while (t--) solve();
  } else {
    solve();
  }
}
