#include<bits/stdc++.h>
using namespace std;
using ll=long long;
#define endl '\n'
#define dbg(x) cerr<<"In Line "<<__LINE__<<' '<<#x<<" = "<<(x)<<endl
ll a[300005],pre[300005],suf[300005],b[300005],c[300005],ans,k;
void solve(int l,int r,ll now){
	if(l==r) return ;
	int mid=l+r>>1;
	pre[l-1]=suf[mid+1]=0;
	int cntl=0,cntr=0;
	for(int i=l;i<=mid;i++) pre[i]=__gcd(pre[i-1],abs(a[i]));
	for(int i=mid;i>=l;i--) suf[i]=__gcd(suf[i+1],abs(a[i]));
	for(int i=l;i<=mid;i++) b[++cntl]=__gcd(pre[i-1],__gcd(suf[i+1],abs(a[i]+k)));
	pre[mid]=suf[r+1]=0;
	for(int i=mid+1;i<=r;i++) pre[i]=__gcd(pre[i-1],abs(a[i]));
	for(int i=r;i>mid;i--) suf[i]=__gcd(suf[i+1],abs(a[i]));
	for(int i=mid+1;i<=r;i++) c[++cntr]=__gcd(pre[i-1],__gcd(suf[i+1],abs(a[i]-k)));
	sort(b+1,b+cntl+1),cntl=unique(b+1,b+cntl+1)-b-1;
	sort(c+1,c+cntr+1),cntr=unique(c+1,c+cntr+1)-c-1;
	for(int i=1;i<=cntl;i++) for(int j=1;j<=cntr;j++) ans=max(ans,__gcd(now,__gcd(b[i],c[j])));
	solve(l,mid,__gcd(now,pre[r])),solve(mid+1,r,__gcd(now,suf[l]));
}
int main(){
	cin.tie(0)->sync_with_stdio(0);
	int t;cin>>t;
	while(t--){
		int n;cin>>n>>k,ans=1;
		for(int i=1;i<=n;i++) cin>>a[i];
		for(int i=n;i;i--) a[i]-=a[i-1];
		for(int i=1;i<=n;i++) pre[i]=__gcd(pre[i-1],abs(a[i]));
		suf[n+1]=0;for(int i=n;i;i--) suf[i]=__gcd(suf[i+1],abs(a[i]));
		for(int i=1;i<=n;i++) ans=max(ans,__gcd(pre[i-1],__gcd(suf[i+1],abs(a[i]+k))));
//		for(int i=1;i<=n;i++) cout<<a[i]<<' ';cout<<endl;
		solve(1,n,0),cout<<ans<<endl;
	}
	return 0;
}