#include<iostream>
#include<cstdio>
#include<cstring>
#include<vector>
#include<map>
#include<algorithm>
#define I inline
#define int long long
using namespace std;

const int N = 300010;
int a[N];
int n,k;
vector<int> g;
map<int,int> mp;

int gcd(int x,int y) {
	if(!y) return x;
	return gcd(y,x%y);
}
I bool check(int x) {
	int cnt=0;
	for(int i=1;i<=n;++i) if(a[i]%x!=0) cnt++;
	if(!cnt) return 1;
	if(k%x==0) return 0;
	for(int i=1;i<=n;++i) {
		if(a[i]%x!=0&&(a[i]+k)%x!=0) return 0;
	}
	bool apr=0; 
	for(int i=1;i<=n;++i) {
		if(a[i]%x!=0) {
			if(apr&&(a[i-1]%x==0)) {
				return 0;
			}
			else apr=1;
		}
	}
	return 1;
}
I void solve() {
	cin>>n>>k; g.clear(); mp.clear();
	for(int i=1;i<=n;++i) cin>>a[i];
	int ng=-1;
	for(int i=1;i<=n;++i) {
		if(ng==-1) ng=a[i];
		else ng=gcd(a[i],ng);
		if(mp[ng]==0) mp[ng]=1,g.push_back(ng);
	}
	ng=-1;
	for(int i=n;i>=1;--i) {
		if(ng==-1) ng=a[i];
		else ng=gcd(a[i],ng);
		if(mp[ng]==0) mp[ng]=1,g.push_back(ng);
	}
	int ans=1;
	for(auto &t:g) {
		if(check(t)) ans=max(ans,t);
	}
	for(int i=1;i<=n;++i) a[i]+=k;
	ng=a[1];
	for(int i=2;i<=n;++i) ng=gcd(ng,a[i]);
	ans=max(ans,ng);
	cout<<ans<<endl;
}
signed main()
{
	int T; cin>>T;
	while(T--) {
		solve();
	}
}