#include <bits/stdc++.h>
using namespace std;
int main() {
  long long int t, i, j, k, m, n;
  t = 1;
  cin >> t;
  while (t--) {
    cin >> n;
    vector<long long int> ar(2 * n, 0), a1(n, 0), a2(n, 0);
    for (long long int i = 0; i < 2 * n; i++) {
      cin >> ar[i];
    }
    sort((ar).begin(), (ar).end());
    long long int c = 0;
    long long int x = ar[(2 * n) / 2];
    long long int y = ar[(2 * n) / 2 - 1];
    long long int ans = 1000000007;
    for (i = 0; i < 2 * n; i++) {
      if (i == (2 * n) / 2 - 1) {
        ans = min(ans, abs(ar[i] - x));
        continue;
      }
      if (i == (2 * n) / 2) {
        ans = min(ans, abs(ar[i] - y));
        continue;
      }
      if (i < n) {
        ans = min(ans, abs(ar[i] - x));
      } else {
        ans = min(ans, abs(ar[i] - y));
      }
    }
    cout << ans << "\n";
  }
  return 0;
}
