Final answer:
The noun 'leaf' is an irregular noun because its plural form is 'leaves', which doesn't follow the standard rule of simply adding -s or -es. 'Kitten' is a regular noun, as its plural is formed by adding -s to become 'kittens'.
Step-by-step explanation:
The question pertains to nouns and their classification as regular or irregular based on how they form their plurals. In English, a regular noun forms its plural by adding -s or -es. An irregular noun has a plural that is not formed by the standard rules and thus must be memorized as it changes vowel, changes word, or remains the same.
Take the noun 'leaf' for example. To make it plural, you do not simply add -s; instead, the word changes to 'leaves', which indicates an irregular change (leaf to leaves). On the other hand, 'kitten' follows the standard rule where you just add -s to make it plural (kittens), making it a regular noun.