#include <bits/stdc++.h>
using namespace std;
int main() {
  int t;
  cin >> t;
  while (t--) {
    int n, x;
    cin >> n;
    vector<int> v, v1, v2;
    for (int i = 0; i < 2 * n; i++) {
      cin >> x;
      v.push_back(x);
    }
    sort(v.begin(), v.end());
    if (n % 2 != 0) {
      for (int i = 1; i < 2 * n; i += 2) {
        v1.push_back(v[i - 1]);
        v2.push_back(v[i]);
      }
    } else {
      v1.push_back(v[0]);
      for (int i = 2; i < 2 * n - 1; i += 2) {
        v1.push_back(v[i - 1]);
        v2.push_back(v[i]);
      }
      v1.push_back(v[2 * n - 1]);
    }
    cout << abs(v1[v1.size() / 2] - v2[v2.size() / 2]) << "\n";
  }
  return 0;
}
