A. object file.
A text file is a file where contents are text characters like English alphabets where each character is encoded as bytes/multi-bytes based on some encoding like ASCII. So, supposing ASCII, to read a text file, we can read 8 bits, and lookup the ASCII character corresponding to that 8 bits in decimal.
A source file is a text file, where the content represent some program in some programming language.
An object file can be defined as given in question.
An executable file is produced by the linker after fixing all inter module dependencies thus making the object file executable. For example, extern references, library linking etc are done by linker and these are absent in object file. Now, executable file contains a sequence of bytes which will be organized into different sections (ELF format in linux) and the code section will be composing of bytes of the form opcode-operand - or proper instructions as understood by the CPU.
PS: All these are non-standard definitions.
