IRA of gain from a sale or exchange of property described in subsection (a) of such section may be treated, at the election of such taxpayer, as a qualified rollover contribution from a Roth IRA for purposes of this section. (B) Limitation The amount of gain that may be treated as a qualified rollover contribution under subparagraph (A) for a taxpayer may not exceed the excess of— (i) the gain from the sale or exchange described in subparagraph (A), over (ii) the amount that would (without regard to paragraph (6) of subsection (b) of such section) be excluded from gross income under subsection (a) of section 121. . (c) Effective date The amendment made by this section shall apply with respect to sales or exchanges of property in taxable years beginning after the date of the enactment of this Act.