Using 8 bit ascii set what would be the total size in bytes of the words 'Computer Science'?

16 bytes

Explanation:

Count one byte (=8 bits) per character, don't forget the space.

The text length is 16 characters, so this fits in 16 bytes. In a C-program you would need an extra 0 byte to mark the end of the string. But that is not asked here.