Before going to solve this question first we have to understand planar density of a crystal lattice.
Planar density of a plane is given defined-
Where N is number of atoms centred in the plane and A is the area of the plane.
As per the question we have been given silver.
We know that silver is a face centered cubic crystal. i.e FCC
The radius of silver [r] is given as 0.144 nm.
.
Hence radius 
We have to calculate the PD of [100] plane of silver.
The area of [100] FCC is 8r^2 where r is the radius silver.
The number of atoms centered on [100] plane is 2.It is so because four atoms will be shared by four corners of the cube and there will be one central atom.Hence there will be only two atoms in one unit cell of [100] plane of silver.
Now we have to calculate the planar density PD.We know that-
![=\frac{2}{8*[0.144*10^{-9}]^2 }](https://tex.z-dn.net/?f=%3D%5Cfrac%7B2%7D%7B8%2A%5B0.144%2A10%5E%7B-9%7D%5D%5E2%20%7D)
[ans]
Are there any options you can choose from?
Answer: C) Label 1: X
Label 2: Z
Explanation: Conductors are those substances which conduct electrical current easily because of the presence of free electrons whereas Insulators do not conduct electrical current as they do not contain free electrons. Some common examples of conductors are copper, aluminum, gold, and silver. Some common examples of insulators are glass, air, plastic, rubber, and wood.
Label 1: Lacks free electrons must be placed in the area marked X as they correspond to insulators.
Label 2: Aluminum is an example of conductor and thus must be labelled in area marked by Z.
Area Y corresponds to semiconductors which have properties intermediate to conductors and insulators.
Answer:
True
Explanation:
In 2019 was taken the first image of a supermassive black hole in the center of the galaxy M87 with the Event Horizon Telescope, which is a network of radio telescope located in different points of the Earth, with the purpose of making a telescope of the size of the Earth.
A radio telescope is an antenna that is capable to perceive the light in the radio part of the electromagnetic spectrum¹.
It is important to notice that in the picture what it can be seen is the effect that the black hole has in the nearby stars.
Key terms:
¹Electromagnetic spectrum: decomposition of light in its different wavelengths (from radio waves to gamma rays).
