For purposes of determining the inclusion ratio, every individual shall be allowed a GST exemption amount which may be allocated by such individual (or his executor) to any property with respect to which such individual is the transferor.

Any allocation under subsection (a), once made, shall be irrevocable.

For purposes of subsection (a), the GST exemption amount for any calendar year shall be equal to the applicable exclusion amount under section 2010 (c) for such calendar year.