Is the sentence correct?
Yes — the sentence is grammatically correct. It means that, when you think about all snakes, rattlesnakes are among those that have the strongest poison.
Step-by-step (easy):
- "Among snakes" tells us we are talking about all snakes.
- "Rattlesnakes" is the subject (the animals we are talking about).
- "are" is the correct verb for a plural subject.
- "some of the most venomous" says that rattlesnakes are in the group of snakes with very strong venom.
Shorter or clearer ways to say it:
- "Rattlesnakes are among the most venomous snakes." (a little clearer)
- "Rattlesnakes are very venomous." (simpler for younger kids)
What does "venomous" mean?
"Venomous" means an animal has poison it can put into another animal by biting or stinging. So a venomous snake can make you sick if it bites you.
Small note: you can add the word "snakes" or "ones" at the end if you want: "Rattlesnakes are some of the most venomous snakes/ones." But your original sentence is already correct and easy to understand.