Correct option is B
The word "limitless" means having no limits or boundaries. In other words, it describes something that is infinite in extent, size, or quantity.
Small (Option A) means not large in size or amount, which is quite the opposite of limitless.
Infinite (Option B) means without any limits or end, which is a perfect synonym for limitless.
Definite (Option C) means clearly defined or having fixed limits, which again is the opposite of limitless.
Indefinite (Option D) means not clearly defined or having no exact limits, but it does not necessarily mean limitless. Indefinite can still imply some uncertainty or vagueness, whereas limitless means completely without boundaries.
So, the correct synonym for "limitless" is Infinite (Option B).