Question

what are the property of alloy which make it different from its constituent metal?

Answer 1

Hello,
Firstly, you should bear in mind that, the 4 main reasons for making alloys are:
1) To improve the strength and hardness of metals,
2) To lower the melting point of the metal,
3) To improve the appearance of the metal and, 
4) To improve the resistance of metals against rusting and corrosion.
Now, answering the question is much easier for, keeping in your head what is in the above, we can say that:
a) Alloys are designed to have properties that are more desirable than those of the elements they contain.
b) Properties such as strength and corrosion resistance may be considerably greater for an alloy than those of the elements they contain.
This is why alloys are more widely used than pure metals.