And electric iron is used to remove wrinkles from clothing. electric iron is made of metal. which property of this substance is most useful for this application

thermal conductivity

Explanation:

An iron works by utilizing the heat generated when passing through a wire. Electricity flows due to the flow of electrons in a material. When the electrons collide with the atoms of the wire there is a transfer of kinetic energy which is realised as heat. If there are many collsions this means that the material has many collions then the material is a bad conductor. If there are fewer collisions then it is a good conductor.

In an iron we need this heat to be transferred to the metal plate of the iron. As metal is a good conductor of heat it is used in an iron.

when two balls of the different masses are dropped from equal height, they reach the ground at the same time .this is because they experience the same acceleration.

the acceleration is independent of mass.

thus when they are dropped they will always maintain the same velocity and travel the same distance (neglect air resistance of course) at the same time.