#include <bits/stdc++.h>
using namespace std;
inline void prep() {
  cin.tie(0);
  cin.sync_with_stdio(0);
};
const double pi = acos(-1.);
long long mod = 1000000007;
long long mymod(long long num) {
  if (num < 0 && !(num % mod == 0)) {
    if (mod == 1) {
      return 0;
    }
    return mod - abs(num) % mod;
  } else {
    return num % mod;
  }
}
const int biggg = 1000000000;
const double eps = .000000001;
int main() {
  prep();
  int t;
  cin >> t;
  for (int x = 0; x < t; x++) {
    int n;
    cin >> n;
    int arr[2 * n];
    for (int i = 0; i < 2 * n; i++) {
      cin >> arr[i];
    }
    sort(arr, arr + 2 * n);
    cout << arr[n] - arr[n - 1] << '\n';
  }
  return 0;
}
