i have created an object with name PS_Detail__c .in this custom object i created a custom field .in this picklist i defined two values Dollar ,Unit.
when i go to P/S Detail Tab for creating a new PS_Detail__c object then i get None also as a value in picklist field .i want only Dollar and Unit as Picklist values .some one please help how to remove this None from Picklist !!
As you have discovered, you cannot make this picklist required at the object level. However, making this field required on the page layout will remove the -None- option from the available options.
To do this, edit the page layout on your object and select the wrench icon next to your field:
Then, you should be able to check the "Required" box in the dialogue box that pops up: