Which of these was a pen-name of Charles Dickens?

Charles Dickens (7 February 1812 – 9 June 1870) is regarded by many as the greatest novelist of the Victorian era. He created some of the world's best-known fictional characters often with unusual and intriguing names. He had an unusual and intriguing name himself. This was commented upon by a contemporary critic: "Mr Dickens, as if in revenge for his own queer name, does bestow still queerer ones upon his fictitious creations." The name that Dickens employed as a pseudonym (pen-name) for several years was "Boz".

Boz was a family nickname. It was adapted from the nickname "Moses", which he had given to his youngest brother Augustus Dickens, after a character in Oliver Goldsmith's "The Vicar of Wakefield". When pronounced by anyone with a head cold, "Moses" became "Boses"—later shortened to Boz. His journalism, in the form of sketches in periodicals, formed his first collection of pieces, published in 1836 as "Sketches by Boz". "Sketches by Boz" proved to be a great success.

Now to the other answer options. "Jez" and "Chaz" are common nicknames often applied to people called "Jeremy" and "Charles", respectively (although not to Charles Dickens). "Phiz" is special. It was the pseudonym of Hablot Knight Browne (10 July 1815 – 8 July 1882) an artist and illustrator. He became Dickens# favourite illustrator for his novels. The accompanying picture is his portrait of Charles Dickens: in effect, "Boz by Phiz".