In question 2 I got tripped up because I assumed sizeof(int) == 8 on a 64 bit system. I also got question 4 wrong because I didn't know that &x gives a pointer to an array of size 5.
Also confusing was the first time I saw this wonderful construct:
void f(int x){
char buf[x + 1];
printf("%zd\n", sizeof(buf))
}
Writing C involves more care than usual because there are so many weird things that are easy to not understand, and not understanding those will cause subtle undefined behavior that allows people controlling the input data to 0wn your computer. Frightening.
Just to make it confusing though, you can't pass an array by value to a function. It gets automatically converted to a pointer. Arrays are unique in the C language in this sense, and it contributes to the illusion that arrays and pointers are the same thing. (Try passing an array by reference, though, and all becomes clear.)