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Thiru MuruganThiru Murugan 

Please explain any one the lookup relationship and Master-details relationship in simple mannar??

Best Answer chosen by Thiru Murugan
SwethaSwetha (Salesforce Developers) 
HI Thiru,

Master-Detail Relationship :

  1. It creates the parent(master) child(Detail) relationship between objects.
  2. If we delete master records then detail (Child) records are deleted.
  3. Rollup-summary field can be created in a master-detail relationship.
  4. We can have maximum 2 master details on an object
  5. Master is required field on the child object.

Look up Relationship :

  1. Look up relationship creates relations between two objects.
  2. If we delete any object then another object is not deleted.
  3. We can have maximum 25 lookups on an object.
  4. Parent is not required in the child record.
  5. Rollup-summary field can be created in this relationship.

To convert master-detail to lookup and vice versa -

You can convert a master-detail relationship to a lookup relationship as long as no roll-up summary fields exist on the master object.

You can convert a lookup relationship to a master-detail relationship, but only if the lookup field in all records contains a value.
Please see http://devfacts.com/master-detail-relationships-vs-lookup-relationships/ which clearly explains how they are different from each other.

Also, the trailhead module explains the same with a real-time example https://trailhead.salesforce.com/content/learn/modules/data_modeling/object_relationships

Hope this helps you. Please mark this answer as best so that others facing the same issue will find this information useful. Thank you