#include <bits/stdc++.h>
using namespace std;
int main() {
  long long t;
  scanf("%lld ", &t);
  while (t--) {
    long long n;
    cin >> n;
    long long r = 2 * n;
    vector<long long> a;
    vector<long long> b;
    vector<long long> c1;
    while (r--) {
      long long c;
      cin >> c;
      c1.push_back(c);
    }
    sort((c1).begin(), (c1).end());
    long long i = 0;
    r = 2 * n;
    cout << abs(c1[n - 1] - c1[n]) << endl;
  }
}
