#include <bits/stdc++.h>
using namespace std;
#define int long long
#define double long double
typedef long long ull;
typedef unsigned long long uull;
typedef pair<int, int> PII;
typedef pair<int,PII> PIII;
typedef __int128 lll;
mt19937 rnd1(random_device{}());
mt19937_64 rnd2(random_device{}());
// uniform_int_depthtribution<int> deptht1(0,2e18);    //定义deptht1为0——100的随机整数
// uniform_real_depthtribution<double> deptht2(-10,10);    //定义deptht2为-10——10的随机浮点数
//#define mp make_pair
//fflush(stdout);
inline void print(__int128 x){//输出模板 
    if(x<0){
        putchar('-');
        x=-x;
    }
    if(x>9) print(x/10);
    putchar(x%10+'0');
}
inline int read()
{
    int X = 0;
    bool flag = 1;
    char ch = getchar();
    while (ch < '0' || ch > '9')
    {
        if (ch == '-')
            flag = 0;
        ch = getchar();
    }
    while (ch >= '0' && ch <= '9')
    {
        X = (X << 1) + (X << 3) + ch - '0';
        ch = getchar();
    }
    if (flag)
        return X;
    return ~(X - 1);
}
const ull mod = 998244353,INF = 2e18;
ull qpow(ull a, ull b)
{
    ull res = 1;
    a %= mod;
    assert(b >= 0);
    for (; b; b >>= 1)
    {
        if (b & 1)
            res = res * a % mod;
        a = a * a % mod;
    }
    return res;
}
inline int gcd(int a, int b) { return b == 0 ? a : gcd(b, a % b); }
inline int lcm(int a, int b) { return a / gcd(a, b) * b; }
const int N = 100010,M = 200100;

int a[N],a1[N];
bool vis[N];
vector<PII> e[N];
vector<int> u,v,x;

void dfs(int u,int k)
{
    if(vis[u]) return;
    vis[u] = 1;
    for(auto [v,t]:e[u])
    {
        if((v>>k)&1)
        {
            a[u] ^= (1ll<<k);
            a[v] ^= (1ll<<k);
            x[t] ^= (1ll<<k);
            dfs(v,k);    
        }
        
    }
}

void solve()
{
    int n;
    cin>>n;
    v.clear(),u.clear(),x.clear();
    for(int i=1;i<=n;i++) cin>>a[i],a1[i] = a[i];
    for(int i=1;i<=n;i++) e[i].clear();
    for(int i=59;i>=0;i--)
    {
        vector<int> p;
        for(int j=1;j<=n;j++) vis[j] = 0;
        for(int j=1;j<=n;j++)
        {
            if(vis[j]) continue;
            dfs(j,i);
            if((a[j]>>i)&1) p.push_back(j);
        }
        if(p.size()>2)
        {
            cout<<-1<<'\n';
            return;
        }
        if(p.size()==2)
        {
            u.push_back(p[0]);
            v.push_back(p[1]);
            x.push_back(1ll<<i);
            int t = u.size()-1;
            e[p[0]].push_back({p[1],t});
            e[p[1]].push_back({p[0],t});
        }
    }
    cout<<u.size()<<'\n';
    for(int i=0;i<u.size();i++)
    {
        cout<<u[i]<<' '<<a1[u[i]]-(a1[u[i]]^x[i])<<'\n';
        a1[v[i]] ^= x[i];
        a1[u[i]] ^= x[i];
    }
    
}   

signed main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
    int t = 1;
    cin>>t;
    while (t--)
        solve();
    return 0;
}