Final answer:
The highest value that can be stored in a BYTE data field is 255.
Step-by-step explanation:
The highest value that can be stored in a BYTE data field is 255 (option a).
A byte is a unit of digital information that consists of 8 bits. Each bit can have two possible values, 0 or 1. Therefore, a byte can represent 2^8 (256) different values. However, since we start counting from 0, the highest value that can be stored in a byte is 2^8 - 1, which is 255.