#include <bits/stdc++.h>
using namespace std;
int main() {
  int t;
  cin >> t;
  while (t--) {
    int n;
    cin >> n;
    long long ip[2 * n];
    long long sum1[n], sum2[n], s1 = 0, s2 = 0;
    for (int i = 0; i < 2 * n; i++) cin >> ip[i];
    sort(ip, ip + (2 * n));
    for (int i = 0; i < 2 * n; i++) {
      if (i % 2 == 0)
        sum1[s1++] = ip[i];
      else
        sum2[s2++] = ip[i];
    }
    if (n % 2 == 1) {
      cout << abs(sum2[s1 / 2] - sum1[s2 / 2]) << endl;
    } else {
      cout << abs(sum2[(s2 / 2) - 1] - sum1[s1 / 2]) << endl;
    }
  }
  return 0;
}
