Which of the following is the correct plural form of this noun: tooth?

The plural form of tooth is teeth. This is an example of an irregular plural noun. While most nouns form their plural by adding -s or -es (like cats or boxes), some nouns, like tooth, change their internal spelling to form the plural.

Here, tooth changes the vowel oo to ee, making teeth the correct plural form. Options like tooths or teeths are incorrect because English rules for irregular plurals don’t allow adding -s or -es to these forms.