"Ik lees een krant en een boek."
Translation:I read a newspaper and a book.
I do not know why Duolingo reported my answer as incorrect, 'cos journal has the same meaning as "newspaper".
No it doesn't. A newspaper reports the news. A journal can be a type of newspaper or magazine that deals with a specific topic, but it can also be (and is more commonly used to mean) a diary or a work in which scientific findings are published. There may be some instances where krant could translate as journal (I'm not sure) but AFAIK it can always translate to newspaper.
Because here, the indefinite article 'een' is used, which means a newspaper. 'The newspaper' would be 'de krant'.