The binary number system is characterized by its use of only two distinct digits, which are 0 and 1. This is the fundamental concept behind the base-2 numeral system, which forms the core language of all digital computers and electronic devices. These digits, often referred to as bits (binary digits), represent two possible states: 0 typically signifies 'off' or 'false' (low voltage), and 1 signifies 'on' or 'true' (high voltage). All data, instructions, and operations within a computer, no matter how complex, are ultimately represented and processed using combinations of these two binary digits.
Option B: 1 and 2 is incorrect. A system using 1 and 2 as its primary digits, possibly along with 0, would constitute a different base system (e.g., base-3 if it includes 0). The binary system is strictly defined by the use of 0 and 1 only.
Option C: 1 and 3 is incorrect. This combination does not define a binary number system. The defining characteristic of binary is its limitation to just two digits, specifically 0 and 1. Any inclusion of other digits changes the base of the numeral system.
Option D: 1 and 5 is incorrect. Similar to the other incorrect options, 1 and 5 are not the digits of the binary system. The uniqueness of binary lies in its minimalist approach of using only the two smallest non-negative integers (0 and 1) to represent all numerical values and logical states.