#include <bits/stdc++.h>
using namespace std;
const int maxn = 2e5 + 5;
const int inf = 1e9 + 7;
int test, n;
int a[maxn];
void solve() {
  cin >> test;
  while (test--) {
    cin >> n;
    for (int i = 1; i <= 2 * n; ++i) cin >> a[i];
    sort(a + 1, a + 2 * n + 1);
    cout << a[n + 1] - a[n] << endl;
  }
}
int main() { solve(); }
