The third law of thermodynamics states that?
a. the entropy of a pure, perfect crystalline substance at absolute zero is not zero.
b. the entropy of a pure, perfect crystalline substance at absolute zero is zero.
c. the entropy of a pure, perfect crystalline substance at absolute zero is negative.
d. the entropy of a pure, perfect crystalline substance at absolute zero is positive.

b. The entropy of a pure, perfect crystalline substance at absolute zero is zero.

Explanation:

There are three laws of thermodynamics which are used to define the physical quantities and parameters like the energy, entropy, temperature. These parameters are used to characterize thermodynamic systems which are at thermal equilibrium.

The third law of thermodynamics:-

According to third law of thermodynamics, the  entropy of the system at absolute zero temperature is a very well-defined constant. Also, for the entropy of the perfect crystalline solid which is at absolute zero is equal to zero exactly.

Thus, the correct option is:- b. The entropy of a pure, perfect crystalline substance at absolute zero is zero.

an electric circuit

electromagnetic shielding is the practice of reducing the electromagnetic field in a space by blocking the field with barriers made of conductive or magnetic materials. shielding is typically applied to enclosures to isolate electrical devices from their surroundings, and to cables to isolate wires from the environment through which the cable runs. electromagnetic shielding that blocks radio frequency electromagnetic radiation is also known as rf shielding.

the shielding can reduce the coupling of radio waves, electromagnetic fields and electrostatic fields. a conductive enclosure used to block electrostatic fields is also known as a faraday cage. the amount of reduction depends very much upon the material used, its thickness, the size of the shielded volume and the frequency of the fields of interest and the size, shape and orientation of apertures in a shield to an incident electromagnetic

from wikipedia