Answer: Shortman.
This is shown when Arnold signs his passport for the class trip. In many episodes, Grandpa calls Arnold "short man." The wrong answer "Bartlett" refers to Craig Bartlett, the show's creator, who said in a 2016 interview that the boy's full name is Arnold Phillip Shortman, and confirmed that the last name would be revealed in "The Jungle Movie." The fact that Grandpa calls Arnold "short man" is a pun on his name, and a reference to the fact that Arnold is shorter than the other kids, while "Football Head" is Helga's nickname for Arnold.
From Quiz: Someone's in the Jungle With Arnold
Answer: Talk-Show Host Sidekick
Woodsperson was the profession given to Harold (although after the tests were mixed up, it was temporarily given to Helga) and Brainy.
From Quiz: "Hey Arnold!" Quizapalooza
Answer: Olga
Olga is precisely 12 years older than Helga.
From Quiz: Hey Arnold! Characters: Helga
Answer: Nadine
Even though they are best friends, Rhonda and Nadine tend to squabble. In the episode "Best Friends", they get into a fight over what they should do their school project on.
From Quiz: Hey Arnold! Characters: Rhonda
Answer: 33
Arnold's best friend, Gerald, is most of the time seen with a red T-shirt with a 33 written in white numbers. The meaning of these numbers is unknown but probably it was just a random choice.
From Quiz: Nick: Hey Arnold!
Answer: Helga
Helga even made a shrine to Arnold made out of chewed gum and is located behind a curtain in her closet.
From Quiz: Hey Arnold!
Answer: Gerald
Gerald often says this about Arnold.
From Quiz: "Hey Arnold" Who Said It?
Answer: He beat her for class president.
Lots of people were shocked at this news, because Gerald was considered to be very cool.
From Quiz: Hey Arnold
Answer: Curly
Curly mentioned that his dad cuts his hair with a bowl in the episode "Cool Party."
From Quiz: Characteristics of "Hey Arnold" Characters!
Answer: G
She rarely mentions it, but she spits whenever she does.
From Quiz: Hey Arnold!
Answer: Monday
After he stole the meat, he had to work in the shop to clean up and then his week was up. Mr. Green finally saw how much Harold enjoyed it, so he ask him, "What are you doing Mondays after school"?
From Quiz: "Hey Arnold" The Cartoon
Answer: Heyerdahl
"Berman" belongs to Harold, "Gamelthorpe" belongs to Thaddeaus (Curly), and "Johanson" belongs to Gerald.
From Quiz: The Phoebe Files
Answer: Helga and Phoebe
When Mr. Simmons said that it was time to work on their Lewis and Clark dioramas and Helga said look who we are stuck with, football head and tall hair boy. Phoebe said that she was looking forward to working with them.
From Quiz: 'Hey Arnold' Episode Trivia
Answer: Gorilla
The episode starts with Arnold and his friends gathered in a room at night. Gerald is finishing up a story about a hairy man and a gorilla, which Stinky describes as "sort of scary". He says he can tell a scarier tale about a "Monkey Cat".
From Quiz: 4.14 "Hey Arnold!" - "Headless Cabbie"
Answer: San Lorenzo.
Arnold first finds out about San Lorenzo in the "The Journal," the final episode of the original series. He discovers a journal written by his father, describing how he met his wife while they were both working in that country, and the mysterious tribe of people they met there. He also mentions that Arnold was born while the couple were in San Lorenzo. In real life, San Lorenzo is not a country, but many Central American countries -- including Colombia, Nicaragua, and Peru -- do have a village or town with that name.
From Quiz: Someone's in the Jungle With Arnold
Answer: Brisket
Ham was the thing Harold stole that resulted in his temporary employment at Green Meats. Prosciutto is one of the meats Harold dreams about in the episode, and Harold tripped on some sausages he was carrying for Mr. Green.
From Quiz: "Hey Arnold!" Quizapalooza
Answer: A woodsperson
Later, Mr. Simmons discovered that Harold's and Helga's aptitude tests got put into the wrong folders, and Helga wasn't meant to be a woodsperson after all.
From Quiz: Hey Arnold! Characters: Helga
Answer: Like an officer for the Fashion Police
Rhonda is always commenting on what everyone is wearing. Almost everyone in her class views her as a mean, self-centered snob.
From Quiz: Hey Arnold! Characters: Rhonda
Answer: Abner
Arnold, unlike many other children, owns a pig, which happens to be a present to his parents from the Green-Eyed People (as featured in the episode "The Journal").
From Quiz: Nick: Hey Arnold!
Answer: Helga
Helga uses this line to threaten people.
From Quiz: "Hey Arnold" Who Said It?
Answer: potato
Arnold was not very pleased with her, because it ruined his experiment.
From Quiz: Hey Arnold
Answer: Sid
In this episode, Sid had a sudden 'phobia' for germs, and Arnold was trying to persuade him to come back to normal and join the frog catching contest.
From Quiz: Characteristics of "Hey Arnold" Characters!
Answer: Orange and Green
When they sing the P.S. 118 song in "Principal Simmons", the colors are mentioned in the song.
From Quiz: Hey Arnold!
Answer: Thaddeus
In episodes "Curly Snaps" and "New Teacher," Curly reveals that his real name is Thaddeus.
From Quiz: "Hey Arnold!" Completely Crazy Curly Quiz
Answer: Lockjaw
The turtle's name was Lockjaw. When Arnold's class went to the aquarium and Arnold saw him, he decided to do something about it. He told his grandma about it and one night they went to the aquarium to rescue him and took him to the ocean.
From Quiz: "Hey Arnold" The Cartoon
Answer: Mow lawns
Gerald tells Arnold that he will make enough money to buy himself a pair of rollerblades by selling Mr. Wacko's watches. Arnold warns that it looks like a rip-off, but Gerald doesn't listen to him. Gerald then tries to convince his dad to sign a form that authorizes the boy to sell watches. His dad is uncomfortable with it and instead suggests that Gerald could earn money by mowing lawns or selling newspapers. Gerald responds that money from those activities is "small change" and ultimately, his father does agree to let Gerald sell watches.
From Quiz: 2.11 "Hey Arnold!" - "The High Life"
Answer: Red
Her hair is curly.
From Quiz: The Phoebe Files
Answer: Yellow
It was yellow. Helga said that she was in charge of all the painting, and Arnold was fighting her for it and then Helga dumped it on him. However, I don't think it was an accident.
From Quiz: 'Hey Arnold' Episode Trivia
Answer: Pink; white
Helga wears this assemblage almost every day, with a few exceptions - she wore a long brown dress at the end of "April Fools' Day" and a white tank top and pink shorts in "Summer Love".
From Quiz: Hey Arnold! Characters: Helga
Answer: Brooke and Buckley
In the episode "Rhonda Goes Broke", Brooke and Buckley lose all of their savings and they, along with Rhonda, have to move to the Sunset Arms, the boarding house that Arnold's grandparents own.
From Quiz: Hey Arnold! Characters: Rhonda
Answer: Eugene
One common gag in "Hey Arnold!" is Eugene's bad luck and the terrible events which happen around him. Among these events are dog attacks, destruction of his belongings (for example, his bicycle) and falling accidents.
From Quiz: Nick: Hey Arnold!
Answer: Sunset Arms
You can see this bit of information on the sign next to the door of the house.
From Quiz: Hey Arnold!
Answer: Stinky
Stinky often uses this phrase in conversation.
From Quiz: "Hey Arnold" Who Said It?
Answer: Hat Girl
Helga hated her job as a model, and the reason she took it was for the free things.
From Quiz: Hey Arnold
Answer: Harold
Harold made it to the finals in the city-wide arm wrestling competition.
From Quiz: Characteristics of "Hey Arnold" Characters!
Answer: Baby Oskar
Baby Oskar was just a visitor while Suzie and her sister Nancy were working.
From Quiz: Hey Arnold!
Answer: Gamelthorpe
Curly tells Principal Wartz in "Curly Snaps" that his last name is Gamelthorpe, but Wartz calls him Mr. Camelthorpe.
From Quiz: "Hey Arnold!" Completely Crazy Curly Quiz
Answer: Ernie and Mr. Hyunh
When Arnold's family was announced to participate on the show, he could only choose two other members. One night at dinner, he finally said that he had made the decision and that he picked Ernie and Mr. Hyunh. Oscar then said, "What about me?" Arnold told him that he could come as an alternate.
From Quiz: "Hey Arnold" The Cartoon