Deleting a parent object record is deleting the child record also in lookup relationship.

Hi @Shiv Murti Pal

 In a normal Lookup Relationship, deleting the parent record does not automatically delete the child record .

 In Salesforce, deleting an Account can also delete its related Contacts due to the special behavior of the standard Account–Contact relationship. A standard Contact-to-Account relationship behaves differently from a custom lookup relationship. 

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Thanks, 

Deepak Sachdeva 

Nubys Technology Pvt. Ltd.