1. His room was as black as pitch with the thick darkness.

2. One of his eyes resembled that of a vulture- a pale blue eye, with a film
over it.

3. I heard all things in heaven and earth. I heard many things in hell.

4. A shriek had been heard by a neighbor during the night.

5. Tear up the planks!-here, here!- it is the beating of his hideous heart!

6. All in vain; because Death, in approaching him, had stalked with his
black shadow before him, and enveloped the victim.

7. It was a low, dull, quick sound- much such a sound as a watch makes
when enveloped in cotton.

8. Yes, he was stone, stone dead.

9. It is merely a cricket which has made a single chirp.

10. It is impossible to say how at first the idea entered my brain, but once
conceived it haunted me day and night.

11. Until, at length, a single dim ray, like the very thread of the spider, shot
from out the crevice and fell upon the vulture eye.

12. A new anxiety seized me- the sound would be heard by a neighbor!

13. It increased my fury, as the beating of a drum stimulates the soldier into
Courage.

which one is a idiom

None of the sentences provided are idioms. An idiom is a phrase that has a figurative meaning that is different from its literal meaning.

The phrase "beating of his hideous heart" (sentence 5) is considered an idiom.

Number 5, "Tear up the planks!-here, here!- it is the beating of his hideous heart!" is an idiom.