Explanation:
In computer architecture, the stack is a region of memory used for temporary storage of data. It follows the Last-In-First-Out (LIFO) principle, which means that the last item pushed onto the stack is the first one to be popped off.

When a PUSH operation is performed, a value is added to the top of the stack. This means that the stack pointer is incremented by the size of the value being pushed. Similarly, when a POP operation is performed, the value at the top of the stack is removed, and the stack pointer is decremented by the size of the value being popped.

To determine the number of bytes stored on the stack during a PUSH or POP operation, we need to consider the size of the value being pushed or popped. The size of the value depends on the data type being stored.

Stack Usage:
- When a PUSH operation is performed, the value being pushed is typically the size of a register or a memory location. For example, if a 32-bit integer is pushed onto the stack, it will occupy 4 bytes of memory.
- When a POP operation is performed, the value being popped is typically the size of the register or memory location it is being stored into. Therefore, it also occupies the same number of bytes as the data type being popped.

Answer:
The number of bytes stored on the stack during one operation of PUSH or POP is 1. This is because the size of the value being pushed or popped is typically 1 byte. However, it is important to note that the size can vary depending on the data type being stored.

Therefore, option 'A' is the correct answer.