#include <bits/stdc++.h>
using namespace std;
using ll = long long;

int main() {
#define int long long
    int T;
    cin >> T;

    while (T--) {
        int N;
        cin >> N;
        vector<pair<int, int>> A(N);
        for (int i = 0; i < N; i++) {
            cin >> A[i].first;
            A[i].second = i;
        }

        if (N >= 201) {
            cout << -1 << '\n';
            continue;
        }

        auto valid = [&](ll x) {
            int cnt = 0;
            int id = -1;
            for (auto [a, idx] : A) {
                if ((a ^ x) < a) {
                    cnt++;
                    id = idx;
                }
            }
            if (cnt != 1) return false;

            for (auto& [a, idx] : A) {
                if (idx == id) {
                    a = (a ^ x);
                }
            }

            return true;
        };

        vector<pair<int, int>> ans;

        bool flag = false;
        while (A.size()) {
            // ranges::sort(A, greater{});
            ranges::sort(A);

            int id = -1;
            for (auto& [a, idx] : A) {
                int b = a;
                a = 0;
                if (valid(b)) {
                    ans.push_back({b, idx + 1});
                    id = idx;
                    break;
                }
                a = b;
            }

            if (id == -1) {
                flag = true;
                break;
            }

            vector<pair<int, int>> nA;
            for (auto a : A) {
                if (a.first) nA.push_back(a);
            }

            swap(nA, A);
        }

        if (flag) {
            cout << -1 << '\n';
        } else {
            assert(ans.size() <= 100);
            cout << ans.size() << '\n';
            for (auto [a, b] : ans) {
                cout << b << ' ' << a << '\n';
            }
        }
    }
}