The correct answer is (A) Arithmetical zero; an arithmetic symbol (0) which signifies naught or zero, but which multiplies or divides numbers by ten, if placed after, or before, them. Also, someone or something of no apparent value, importance, or influence; a nonentity. In addition, a method of transforming text in order to conceal the meaning by systematically transposing letters or substituting letters, special symbols, etc., or the key to it. A cipher can also mean any Arabic numeral or figure.

Cipher comes from Middle English siphre, Old French cyfre, Arabic sifr (nothing), cifr (zero), Latin ciphra

Examples of use:

• The spy used a cipher to decode the secret message that was left for him
• The evening transmission was sent as a cipher.