A 32-bit microprocessor has a word length equal to

A 32 bit processor has a word length of 32 bits, which equals 4 bytes.

A value of 2 bytes is only 16 bits, too small.

A value of 32 bytes would be 256 bits, far too large.

A value of 8 bytes is 64 bits, matching a 64 bit word instead.

Since one byte is 8 bits, 32 divided by 8 gives 4 bytes.

Add-on: word length is the amount of data the processor handles in one step.