#include <bits/stdc++.h>
using namespace std;
const int N = 1e5 + 7;
const int INF = 2e9 + 7;
int a[N * 2];
int main() {
  int T;
  scanf("%d", &T);
  while (T--) {
    int n;
    scanf("%d", &n);
    for (int i = 0; i < n * 2; ++i) scanf("%d", &a[i]);
    sort(a, a + n * 2);
    int ans = INF;
    for (int i = 0; i < n * 2; ++i) {
      int j = (n * 2 - 1) / 2;
      if (j >= i) j += 1;
      ans = min(ans, abs(a[i] - a[j]));
    }
    printf("%d\n", ans);
  }
}
