When a key is pressed on keyboard, which standard is used for converting the…

A character-encoding standard is a fixed table that maps each character in its defined repertoire -- letters, digits, punctuation marks, and common control codes -- to a unique binary representation, so that a character can be represented and processed as digital data.

In practice, keyboard hardware first reports its own scan or HID code for a keypress; software then maps that hardware event to a character. For representing standard printable characters and common control codes as bits, the historical -- and, for this question's exam convention, the intended -- character-encoding scheme is ASCII (American Standard Code for Information Interchange), which assigns a fixed 7-bit binary code to each such character. (Many modern systems represent that mapped character in Unicode instead, and several keys such as modifiers or function keys carry no ASCII code at all; this question follows the classic exam convention of naming ASCII as the keystroke-to-bits standard.)

• ANSI (American National Standards Institute) is the US standards-accrediting body that approved ASCII as an American National Standard; it is not itself a bit-level encoding scheme, which is why it is sometimes confused with ASCII.

• EBCDIC is an older 8-bit encoding IBM built for its own mainframe computers; it is not the encoding this question's exam convention associates with standard keyboard input.

• Per that same exam convention, exactly one of the listed terms is treated as the keystroke-to-bits standard, which is why a compound ('more than one') or empty ('none') selection does not fit the intended single answer here.

So, following that exam convention, the standard used to convert a keystroke into its corresponding bits is ASCII.