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

int main() {
    int T;
    cin >> T;

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

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

        auto valid = [&](ll x, vector<int> a) {
            int cnt = 0;
            int id = -1;
            for (int i = 0; i < N; i++) {
                if ((a[i] ^ x) < a[i]) {
                    cnt++;
                    id = i;
                }
            }
            if (cnt != 1) return -1;
            return id;
        };

        vector<pair<int, int>> ans;

        auto dfs = [&](auto&& dfs, vector<int> a) -> bool {
            if (ranges::max(a) == 0) {
                return true;
            }

            for (int i = 0; i < N; i++) {
                int b = a[i];
                a[i] = 0;
                int id = valid(b, a);
                // xor(a)=b
                if (id != -1) {
                    int c = a[id];
                    a[id] = a[id] ^ b;
                    // xor(a)=0
                    if (dfs(dfs, a)) {
                        ans.push_back({i, b});
                        return true;
                    }
                    a[id] = c;
                }
                a[i] = b;
            }

            return false;
        };

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