Final answer:
Setting 100 as the default value for the rate field ensures that all new records will have that value unless specified otherwise, but does not alter existing records.
Step-by-step explanation:
The statement that if you set 100 as the default value for the rate field, 100 is inserted in the Rate field for all new records only, is true. Setting a default value in a database field means that every time a new record is created, if no other value is specified for that field, the default value will automatically be applied. However, this change does not affect any existing records that were entered into the database before the default was set. Default values are commonly used in database design to ensure consistency in data entry, especially for fields that have a common value that is frequently used.