The correct answer is option 'C' - Binary numbers.


The tape used on NC (Numerical Control) machine tools contains a system of instructions that are based on binary numbers.


Numeric instructions use only numbers to represent the commands and parameters for the machine tool. For example, a numeric instruction could be "10" which represents a specific movement or operation on the machine.


Alphanumeric instructions use both letters and numbers to represent the commands and parameters. These instructions may provide more detailed information or specific settings for the machine tool. For example, an alphanumeric instruction could be "G01" which represents a specific linear interpolation or "M03" which represents the command to start the spindle in a clockwise direction.


Binary numbers are a base-2 number system that uses only two digits: 0 and 1. In the context of NC machine tools, the binary numbers are used to represent the instructions and parameters. Each binary digit is called a bit, and a sequence of bits represents a specific command or value. These binary numbers are read and interpreted by the computer control system of the machine tool.


Binary coded decimals (BCD) is a binary representation of decimal numbers. It is a way to represent decimal digits using a binary code. In the context of NC machine tools, BCD may be used to represent decimal numbers or specific values that are required for the machine operations.


In summary, the tape used on NC machine tools contains instructions that are based on binary numbers. These binary numbers represent the commands and parameters for the machine tool operations. Numeric, alphanumeric, and binary coded decimals may also be used in conjunction with binary numbers to provide more detailed instructions and values.