Question

To make powerful magnets, the alloy used is:
A. Alnico
B. Aluminum
C. Cobalt
D. Ferrites

Answer 1

Magnets are rocks or metals that create an invisible field around them. This field attracts other magnets or metal towards it. The ends of the magnetic field are called poles. Poles are the part of the magnetic field where the magnetic field is concentrated. There are two poles in every magnet called the North Pole and the South Pole.
There are three types of magnets
Permanent Magnet
Temporary magnets
Electromagnets

Complete step by step solution:
So the most powerful magnets are made up of alnicos. Alnicos are a class of iron alloys made up of aluminum, nickel, and cobalt in addition to iron. Because they are a class of iron alloys they are ferromagnetic in nature. They were the strongest permanent magnet type before rare earth magnets were found. Permanent magnets emit a magnetism without the need for any electrical power or external source of magnetism as in the case of electromagnets and temporary magnets.
Alnicos are used for making permanent magnets because of high coercivity and high retentivity. The term coercivity means the resistance offered against demagnetization. So as large is coercivity, as long the magnetization retains. The term retentivity means the ability of the magnetic material to retain magnetism even when the magnetizing field is absent. So obviously, retentivity should be high for a permanent magnet. These two characteristics make the alnico alloys be used in the production of permanent magnets.
Hence, option A is correct.

Additional Information.
As we said earlier, in addition to permanent magnets there are other two types of magnets. They are temporary magnets and electromagnets. Temporary magnets are those which exhibit magnetism when they are attached or brought closer to some other materials that emit magnetic fields. These temporary magnets lose their magnetism once they are separated by the materials that emit a magnetic field. And electromagnets need electricity in order to emit magnetism.

Note:
The magnetic field strength at the poles of the alnico magnets is found to be $1500gauss$ which are approximate $3000$ times Earth’s magnetic field. But, after the discovery of rare earth magnets, alnicos are not widely used for permanent magnets. Neodymium magnets are the strongest existing rare earth magnets that are widely used in industrial products.