(a) A bond with zero interest rate but with highest liquidity value for which investors get other concessions like tax breaks

(b) A bond with zero coupon rates which is sold at a price lower than its face value and investors get face value price at maturity

(c) A special category of bonds used as 'express money' to finance immediate needs of the economy which carries zero interest but gives tax credits to investors in their income tax returns

(d) A kind of bond which is generally issued by governments in the times of financial crises to the high income group citizens which carry no interest but investors get tax concessions for investing in it