Final answer:
The suffix of the word younger is -er.
Step-by-step explanation:
The suffix of the word younger is -er. A suffix is a group of letters added to the end of a word to change its meaning or function. In this case, the suffix -er is added to the word young to form the comparative degree, indicating that someone or something is more young or youthful than another.
Learn more about Suffixes in English words