Correct spelling, explanation: the correct spelling is too small. Too is used to indicate excess or an extent beyond what is desirable or appropriate, while small is the adjective describing the size. Together, they form the phrase too small, meaning something is smaller than desired or necessary. On the other hand, to is a preposition with various uses, such as indicating direction, purpose, or extent. However, in this context, to small is not grammatically correct because to is not used to modify an adjective like small. It doesn’t convey the intended meaning of being smaller than desired or appropriate.

Definition of too small:
phrase, describes something that is smaller in size or extent than is desired, appropriate, or necessary
The font size on this website is too small to read.
The room is too small for all the guests.

Collocations with too small:
Some most commonly used collocations include:
1. Too small for: used to describe something that does not fit or is not suitable for a particular purpose or person.
The shoes were too small for her feet, so she had to exchange them for a larger size.
2. Too small to: used to describe something that is not large enough or lacks the necessary size for a specific action or function.
The box was too small to hold all the items, so we had to find a bigger one.
3. Too small a(n): used to express that a quantity or amount is insufficient or inadequate for a given purpose.
A single slice of cake is too small a portion to satisfy my appetite.
4. Too small to notice: used to describe something that is not big enough or prominent enough to be easily seen or recognized.
The scratch on the car was too small to notice at first, but it became more visible over time.

Incorrect spelling, explanation: the phrase to small is considered a mistake because it doesn’t follow the correct grammatical rules in English. The word to is a preposition with various meanings, such as indicating direction, purpose, or extent, but it is not used to modify an adjective like small. Instead, the correct adverb to use in this context is too. Too is an adverb that means excessively or more than necessary. When combined with the adjective small, it forms the phrase too small, which means something is smaller than what is needed or suitable.