Option B is plain stupid. Ignore it.
Option A isn't necessary, because programming language C does implicit typecasting.
So, we're left with Options C and D
Now, dangling pointer is (using) a pointer that points to nowhere / garbage value.
Memory leak is a piece of memory in the heap, that can't be accessed because the pointer for it is deleted off.
Now, see the code. Are we clearing a pointer? Yes, we are.
After doing so, we're terminating the program, and not using the pointer x again. We'll never access x, which currently is freed (points to nowhere). So, no dangling pointer.
Is there a memory leak?
Trick: To immediately detect a memory leak in the code, try to find two successive assignments to a pointer, without clearing the pointer first.
int *x = malloc(sizeof(int));
x = assignval (x,0);
We assigned the pointer a heap-address and a value.
Then, we did this inside the if-statement
x = (int *)malloc(sizeof(int));
x = assignval (x,10);
New memory location assigned to x, and x points to it now. Nothing points to the previous location, hence memory leak