The dictionary bought by her is very heavy.

In the given sentence, dictionary is a general name of a book.

Hence, the word dictionary is a common noun.

Jack works as a clerk.

In the given sentence, clerk is a general term used for a person and Jack is a person’s name.

Hence, the word clerk is a common noun and Jack is a proper noun.

The roses are placed in a basket.

In the given sentence, roses and basket are the general terms used for things.

Hence, the words roses and basket are common nouns.