In zero coupon bonds, increase in duration with respect to maturity must be at

In zero coupon bonds, increase in duration with respect to maturity must be at decreasing rate. A zero-coupon bond is a debt security instrument that does not pay interest. Zero-coupon bonds trade at deep discounts, offering full face value (par) profits at maturity. The difference between the purchase price of a zero-coupon bond and the par value, indicates the investor's return.