Fill in the blanks.
(i) Zero has _________ reciprocal.
(ii) The numbers ___________ and __________ are their own reciprocals.
(iii) The reciprocal of is _________.
(iv) Reciprocal of , where is _________.
(v) The product of two rational numbers is always a ______________.
(vi) The reciprocal of a positive rational number is _______________.