What are various standard exceptions that salesforce throws?

There are number of Exception,

• AsyncException

Any problem with an asynchronous operation, such as failing to enqueue an asynchronous call.

• CalloutException

Any problem with a Web service operation, such as failing to make a callout to an external system.

• DmlException

Any problem with a DML statement, such as an insert statement missing a required field on a record.

• JSONException

Any problem with JSON serialization and deserialization operations.