Two dimensional arrays(dynamically) if condition for null in c

Hi people I created an array that is two-dimensional dynamically. I want to determine which row empty but my syntax knowledge is insufficient. Thank you in advance for your interest.

There is my code:

#include <stdio.h>
#include <stdlib.h>
int main(void)
{
    int i,j,*x,y=0;
    int** p=malloc(sizeof(int*)*4);
    for(i=0;i<3;i++)
        p[i]=malloc(sizeof(int)*3);
    for(i=0;i<3;i++)
    {
        for(j=0;j<3;j++)
            p[i][j]=(y++);
    }
    x=NULL;
    for(i=0;i<4;i++)
    {
        // Fourth index shouldn't be NULL?
        if(p[i]==x)
            printf("NULL");
        else
            printf("Not null");
    }
    for(i=0;i<4;i++)
        free(p[i]);
    free(p);
    return(0);
}