Which of the following statement is TRUE? A) Stack pointer decremented by one when PUSH instruction executed. B) Stack pointer incremented by one when PUSH instruction executed. C) Stack pointer decremented by two when PUSH instruction executed. D) Stack pointer incremented by two when PUSH instruction executed.

The correct statement is A) Stack pointer decremented by one when PUSH instruction executed.

Here's why:

In computer science, a stack is a particular kind of abstract data type or collection in which the principal (or only) operations on the collection are the addition of an entity to the collection, known as push and removal of an entity, known as pop. The relation between the push and pop operations is such that the stack is a Last-In-First-Out (LIFO) data structure.

In a LIFO data structure, the last element added to the structure must be the first one to be removed. This is exactly the principle followed by stack data structure.

When a PUSH instruction is executed, the stack pointer is decremented to create space for the new item and then the item is inserted at the new top of stack. Hence, the statement "Stack pointer decremented by one when PUSH instruction executed" is true.