Step 1: Identifying the Error.
The sentence "Mohan's father purse has been stolen" contains a grammatical error. The possessive "Mohan's father" is followed incorrectly by "purse." The possessive form should be used with a noun indicating possession, and in this case, it should be phrased as "Mohan's father's purse."
Step 2: Correcting the Sentence.
The corrected sentence should read:
Mohan's father's purse has been stolen.
Final Answer: \[ \boxed{\text{Mohan's father's purse has been stolen.}} \]