#include <bits/stdc++.h>
using namespace std;
vector<long long int> v1, v2, v3;
string s1, s2, s3;
int main() {
  long long int a, b, c, d, e, f, i, j, k, cnt1 = 0, cnt2 = 0, sum1 = 0,
                                           sum2 = 0, chk1 = 0, chk2 = 0, T;
  cin >> T;
  for (i = 0; i < T; i++) {
    cnt1 = 0, sum1 = 0;
    v1.clear();
    cin >> a;
    for (j = 0; j < a + a; j++) {
      cin >> b;
      v1.push_back(b);
    }
    sort(v1.begin(), v1.end());
    cout << abs(v1[a - 1] - v1[a]) << endl;
  }
  return 0;
}
