Can someone please explain WHY the code is valid or invalid for the following question? I don't understand why. Please explain clearly and thoroughly. The question and its answer is given below:

Q2) The following table assumes the declaration of int nums [10];. In each table row there is an example. Indicate whether or not the code is valid (i.e., is syntactically correct and exhibits correct, well-defined behaviour) or invalid (i.e., is syntactically incorrect and/or exhibits undefined behaviour). Example Code Example Is Valid Code Example is Invalid Code a) int *a = nums; a -= 1; b) int *b = nums; b - = 2; c) int *c = nums; C += 9; d) int *d = nums; d += 10; int *e = nums; e += 11; f) int *f = nums; f += 12