(a) Two bytes read/write at a time.
Reason: There are two types of I/O stream. One is a byte stream, and the other is the character stream. The Byte stream is used to perform input or output 8-bit (equals to 1 byte) Unicode bytes whereas, the Character stream is used to read or write a 16-bit (equals to 2 bytes) Unicode character.
Therefore, a single operation of character stream performs two bytes read/ write at a time.