Organic (aldehyde)

monosaccharides(C6H12O6) can be aldehyde or ketone. If it has H-C=O as a fountional group, then it is aldehyde (biological term : glucose). Naturally, glucose exist in forms of both 6-C ring (without double bond O) and 6-C chain (with double bong O). Glucose' s reducing power is due to the =O fountional group, which have a high tendency to donate e- (itself being oxidised) . Also, the the carbon chain is e- rich and this further increas the reducing power of glucose. When it was mixed with weak reducing agent, it donate e- more readily and thus it have reducing power.

when aldehyde dissolve in water, it will form a chain structure instead of a ring struture, it is a kind of property that glucose and other monosaccharides have.