#include <iostream>
#include <algorithm>
#include <vector>
#include <set>
#include <cmath>
#include <map>
#include <string>
#include <fstream>
#include <queue>

using namespace std;


typedef long long ll;


int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
    int tt;
    cin >> tt;
    while (tt--) {
        int n;
        cin >> n;
        vector <int> a(n * 2);
        for (int i = 0; i < n * 2; ++i) {
            cin >> a[i];
        }
        sort(a.begin(), a.end());
        cout << a[n] - a[n - 1] << endl;
    }

}