Question

His father is a farmer (underline proper &common noun)
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Answer 1

There is no proper noun in this sentence. Proper nouns are special names, here, ‘father’ can be used to refer to any male person with a child and there are also many farmers. If there was name of a father or a particular type of farmer given, there would’ve been a proper noun in this sentence.
There are two common nouns in this sentence- father and farmer.