Well, The first sentence is correct and the second is not. the second one means like : "my pen this black" Looks weird hah!. هو is considered a demonstrative or personal pronoun you can say "هو أسود " means "He is black" we don't mention the Verb to BE in Arabic. شكرا instead of سكرا

Salam. I totally agree with all answers given. I just want to add something to be confused and to understand more what's the real difference between the two sentences. First, I have to correct the sentences. قلمي أسود قلمي هو أسود Now grammatically the both sentences are correct. The first one it's a noun sentence جملة إسمية and it gives you an information about the pencil you are using is black. The second one is correct grammatically, because you do make it as جملة إسمية المبتدأ is قلمي الخبر is هو أسود Therefore, it's useless to make. There is another way to make a great sense in Arabic, is using الأسود in that case, you are making a confirmation about the color of your pencil, and that means there is no certitude about that. As you know ال using for definite something. Hope it helps you understanding! Salam Sadeqi

in Arabic we do not use such pattern قلمي هو أسود we do not need هو here , it seems like literal translation to my pen is black and you put هو to replace is. But it is better to replace is with إن and my pen is black will be إن قلمي أسود here - too - we do not need such form very often because it suggestion kind of affirmation. in a word Arabic is similar to Russian language, it does not use (is,am,are) in the present tense.

The defferance is : the 1st : true the 2nd : true but the word (هو) is redundant You mustn't have to add (هو) to the adjective.

the difference is in grammer قلمى أسود the word قلمى is a subject and the word أسود is predicate. قلمى هو أسود the word قلمى is a first subject and هو is a second subject and أسود is a predicate for the second subject and the second subject with its predicate make a Nominal sentence which is considered as a predicate for the first subject