1. You do not need to use any article before the word "apple". Your question is fine (well-formed): "Are there some pieces of apple in the salad?". I personally would say: "Are there some pieces of apple in that salad?" 2. You should use the article "a" instead of "the": "I saw on my friend's instagram a photo of a salad". I hope this answers your question.

Hi Alexey, Situation: I saw [a picture] of [a/some] salad [on my friend's Instagram.] "Are there some pieces of apple in the salad?" 1) Should I use an article before the word "apple"? An article is unnecessary here even though "apple" is a countable noun. This is because you are already using a unit of measure (i.e. pieces of). Other examples: crates of apples (NOT crates of the apples). 2) Should I use an article before the "salad" word in the sentence "I saw on instagram of my friend the photo of the salad."? Yes, you should be using an article before the word "salad". I presume you are referring to "salad" in the picture for the first time, and has never seen it before. In this case, a definite article (the) should not be used here. Therefore, you can use a quantifier such as "some" or "a" to describe a serving of salad: I saw [a picture] of [a] salad [on my friend's Instagram.] / I saw [a picture] of [some] salad [on my friend's Instagram.] Just as a side discussion, we use the structure (xx's yy) instead of (yy of xx) when we are referring to a person's possession (e.g. "my friend's Instagram" instead of "Instagram of my friend". On the other hand, we tend to use (yy of xx) with inanimate things (e.g. "the dial of the oven is faulty" instead of "the oven's dial is faulty") I hope this helps.