Materials and Their Applications

In chemistry, a mixture is a material system made up of two or more different substances which are mixed but are not combined chemically. A mixture refers to the physical combination of two or more substances on which the identities are retained and are mixed in the form of solutions, suspensions, and colloids.

Note that a mixture:

• consists of two or more different elements and/or compounds physically intermingled,
• can be separated into its components by physical means, and
• often retains many of the properties of its components.

Synthetic materials in daily life are:

A magnetic core is a piece of magnetic material with a high permeability used to confine and guide magnetic fields in electrical, electro-mechanical and magnetic devices such as electromagnets, transformers, electric motors, generators, inductors, magnetic recording heads, and magnetic assemblies. It is made of ferromagnetic metal such as iron, or ferrimagnetic compounds such as ferrites.
The magnetic field is often created by a coil of wire around the core that carries a current. The presence of the core can increase the magnetic field of a coil by a factor of several thousand over what it would be without the core. The use of a magnetic core can enormously concentrate the strength and increase the effect of magnetic fields produced by electric currents and permanent magnets. 
The properties of a device will depend on the following factors:

• The geometry of the magnetic core.
• The amount of air gap in the magnetic circuit.
• The properties of the core material like permeability and hysteresis.
• The operating temperature of the core.
• Whether the core is laminated to reduce eddy currents.

Answer is D.

Soft iron are ferromagnetic materials made of iron which can be magnetized and demagnetized easily. This is an advantage in transformers because in transformers, we're constantly varying magnetism of the core. This is important because without the change of magnetism of the core, there wouldn't be any voltage induced in the second circuit (the output)! Hence, using a soft iron would allow the magnetism of the core to be changed easily, lessening the amount of energy lost and increasing the efficiency of the transformer. 
Hence, soft iron is used to make core of the transformer.

Soft iron provides the best material for the core of a transformer as its permeability $(\mu)$ is very high. Its hysteresis curve is of small area and its coercivity is very low.

Extensive green roofs are the most common type of green roof. They are characterized by a thin layer of growing medium and low-maintenance plants. Extensive green roofs are relatively easy to install and maintain.

There are three main types of green roofs: extensive green roofs, intensive green roofs, and semi-intensive green roofs. Extensive green roofs are characterized by a thin layer of growing medium and low-maintenance plants. Intensive green roofs are characterized by a thicker layer of growing medium and a wider variety of plants. Semi-intensive green roofs fall somewhere in between extensive and intensive green roofs.

Dry leaves are easily combustible and can be ignited with a spark or friction. They are often used as tinder to start a fire.

Composite materials are made from two or more different materials, and they can be stronger, lighter, and stiffer than their individual components.

The two main types of composite materials are matrix composites and reinforced composites. Matrix composites consist of a matrix material and a reinforcing material, while reinforced composites consist of a reinforcing material and a matrix material.

Common matrix materials include metals, ceramics, and polymers.

Common reinforcing materials include fibers, particles, and flakes.

Composite materials can have high strength, high stiffness, and low weight.

Composite materials are used in a wide variety of applications, including aerospace, automotive, and construction.

Recent advances in composite materials include the development of new matrix materials, new reinforcing materials, and new manufacturing techniques.