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

#define rep(i, a, b) for(int i = a; i < (b); ++i)
#define all(x) begin(x), end(x)
#define sz(x) (int)(x).size()
#define F first
#define S second
#define pb push_back
typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vi;

int hp(int x){
	int i = 0;
	while((1ll<<i) <= x)i++;
	return i;
}

int main() {
	cin.tie(0)->sync_with_stdio(0);
	cin.exceptions(cin.failbit);
	int tests;cin>>tests;
	while(tests--){
		int n;cin>>n;
		vi a(n);rep(i,0,n)cin>>a[i];
		if(n>200){
			cout<<-1<<endl;
			continue;
		}
		vi inds(n);iota(all(inds),0);
		sort(all(inds),[&](int i, int j){ return a[i]>a[j];});
		// rep(i,0,n)cout<<a[inds[i]]<<' ';
		// cout<<'\n';
		vector<pii> ops;
		bool bad = false;
		while(sz(inds)){
			if(sz(inds)>2 && hp(a[inds[0]])==hp(a[inds[2]])){
				bad=true;
				break;
			}
			// rep(i,0,sz(inds))cout<<a[inds[i]]<<' ';
			// cout<<'\n';
			// cout<<"xor  by "<<a[inds[1]]<<endl;
			ops.pb({inds[0],a[inds[0]]-(a[inds[0]]^a[inds[1]])});
			a[inds[0]]^=a[inds[1]];
			inds.erase(inds.begin()+1);
			if(a[inds[0]]==0)inds.erase(inds.begin());
			sort(all(inds),[&](int i, int j){ return a[i]>a[j];});
		}
		if(bad)cout<<"-1\n";
		else{
			cout<<sz(ops)<<'\n';
			for(pii op : ops)cout<<op.F+1<<' '<<op.S<<'\n';
		}
	}
}