Thank you very much. I included my corrections in brackets, when necessary.

1)The front door is where Dr Jekyll is seen and represents his public face.
2)His friend moves like a guttering candle which is about to go out.He describes the face of his dying friend, his skin which is starting to fall off and his eyes which are writhing (or writhing eyes).
3)The poet is horrified by chemical warfare since he has seen his friend’s death. ( the poet has been horrified by chemical warfare ever since he saw his friend dying)
4)There is a similarity with the myth of Faust ( better: between Dorian and Faust) since they both sold (not sell) their souls to the devil to have their desires satisfied. (can you say “in exchange for absolute knowledge and eternal youth respectively). Killing the picture means . (is the gerund correct?)
5)He realizes his personality is made of two parts. The duality of man’s nature is also represented by the two sides of the doctor’s house: the front entrance is nice whereas the rear one is dark and ugly.
6)In the first part of the novel Lord Henry’s point of view is adopted/used, whereas in the second one Dorian’s. Life must be lived for art (better for art’s sake) forgetting moral responsibility.

1. OK

2. Owen describes the face of his dying friend, whose skin is starting to fall off and whose eyes are writhing. His friend moves like a guttering candle.
Please note ALL corrections. You don't need "which is about to go out" because that's what "guttering" means. You cannot place "friend" and "his skin" directly next to each other because they are NOT appositives. Etc.

3. Either phrasing is fine; just don't mix the two.

4. Yes, use the "between" phrasing; use "sell" not "sold." The first sentence here is terribly awkward. Try this instead:
There is a similarity between Dorian and Faust since they both sell their souls to the devil to have all their desires met.

5. Capital T -- comma needed

6. Comma needed; use "adopted"; use "for art's sake"

1) The front door is where Dr Jekyll is seen and represents his public face.

Explanation: To arrive at the answer, we can analyze the symbolism in the text. In the story, the front door is the entrance that Dr Jekyll uses to interact with the public, where he presents himself as a respectable and upstanding member of society. This represents his public face or persona.

2) His friend moves like a guttering candle which is about to go out. He describes the face of his dying friend, his skin which is starting to fall off, and his eyes which are writhing (or writhing eyes).

Explanation: Here, the writer is using vivid imagery to describe the deteriorating physical condition of his dying friend. To understand the phrase "moves like a guttering candle which is about to go out," we can break it down. First, the phrase "guttering candle" refers to a candle that is flickering or wavering, similar to how the friend's movements are frail and uncertain, like a dying flame. The phrase "about to go out" further emphasizes the impending extinguishment, highlighting the friend's imminent death.

3) The poet has been horrified by chemical warfare ever since he saw his friend dying.

Explanation: To determine how the poet feels about chemical warfare, we can look at the phrase "ever since he saw his friend dying." This suggests that the poet's horror towards chemical warfare began after witnessing his friend's death.

4) There is a similarity between Dorian and Faust since they both sold their souls to the devil to have their desires satisfied. Killing the picture means . (Is the gerund correct?)

Explanation: To establish the similarity between Dorian and Faust, we can examine the common element of both characters selling their souls to the devil. This exchange was made to fulfill their respective desires: Faust desired absolute knowledge, and Dorian sought eternal youth. As for "killing the picture means ," the gerund "killing" is correct here. It implies that destroying the picture, which ages and bears the marks of Dorian's sins, is akin to self-destruction for Dorian.

5) He realizes his personality is made of two parts. The duality of man’s nature is also represented by the two sides of the doctor’s house: the front entrance is nice, whereas the rear one is dark and ugly.

Explanation: By examining the text, we can understand that the character realizes his personality consists of two distinct parts. This reflection aligns with the concept of the duality of man's nature. To further support this duality, the text describes the doctor's house having two contrasting sides: the front entrance, which is described as nice, and the rear entrance, which is described as dark and ugly. This juxtaposition symbolically represents the opposing aspects of the character's nature.

6) In the first part of the novel, Lord Henry’s point of view is adopted, whereas in the second one, it shifts to Dorian’s. Life must be lived for art's sake, forgetting moral responsibility.

Explanation: To understand the narrative perspective in the novel, we can examine the statement that Lord Henry's point of view is adopted in the first part while it shifts to Dorian's perspective in the second part. This implies that the story initially focuses on Lord Henry's viewpoint and later transitions to Dorian's perspectives and experiences. Regarding the phrase "Life must be lived for art's sake, forgetting moral responsibility," it highlights the idea that the pursuit of artistic endeavors takes precedence and leads to a disregard for moral obligations.