On hammering, metals change into thin sheets. The property of metals is known as:
(a)- Ductility
(b)- Sensitivity
(c)- Conductivity
(d)- Malleability

Hint: Metals have many properties like drawing into thin sheets, drawing into wires, becoming hot on heating, can be used in electrical appliances, etc, and these properties are known as ductility, malleability, conductivity, etc.

Complete answer:
Metals have many properties like drawing into thin sheets, drawing into wires, becoming hot on heating, can be used in electrical appliances, etc and these properties are known as ductility, malleability, conductivity, etc.
So when the metals are hammered, any shape of the metal starts to convert into thin sheets, and this property is known as malleability. For the conversion of metals into thin sheets, pressure is applied to the metals. When the metals are drawn into sheets, the thin sheets are known as a metal leaf. Gold-leaf is a well-known example of metal-leaf.
Some of the common examples of malleable metals are gold, silver, copper, lead, aluminium, and iron. But gold and silver are the most malleable metals. That's why gold and silver are used in jewelry and many decorative items.
If the compound is a non-malleable metal or element, then on hammering the metal or element, it will break into pieces. This is observed in non-metals.

So the correct answer is an option (d)- Malleability.

Note:
Mostly the metals which are malleable, also show the property of ductility. When a compound or element can be drawn into wires, then the property is called ductility. Lead is an example of having the property of malleability but not the property of ductility.