#include <bits/stdc++.h>
using namespace std;
double EPS = 1e-9;
long long INF = 1000000000000000005ll;
double PI = acos(-1);
inline string IntToString(long long int a) {
  char x[100];
  sprintf(x, "%lld", a);
  string s = x;
  return s;
}
inline long long int StringToInt(string a) {
  char x[100];
  long long int res;
  strcpy(x, a.c_str());
  sscanf(x, "%lld", &res);
  return res;
}
inline string uppercase(string s) {
  int n = (int)s.size();
  for (long long int i = 0; i < n; i++)
    if (s[i] >= 'a' && s[i] <= 'z') s[i] = s[i] - 'a' + 'A';
  return s;
}
inline string lowercase(string s) {
  int n = (int)s.size();
  for (long long int i = 0; i < n; i++)
    if (s[i] >= 'A' && s[i] <= 'Z') s[i] = s[i] - 'A' + 'a';
  return s;
}
bool sortcol(const vector<long long int>& v1, const vector<long long int>& v2) {
  return v1[0] > v2[0];
}
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  long long int t;
  cin >> t;
  while (t-- > 0) {
    long long int n;
    cin >> n;
    n *= 2;
    long long int a[n];
    for (long long int i = 0; i < n; i++) cin >> a[i];
    sort(a, a + n);
    cout << a[n / 2] - a[n / 2 - 1] << '\n';
  }
  return 0;
}
