Answer:
Coordination number:
Coordination number can be defined as the number of nearest atoms which touch the central atom.In simple word the number of neighbours atoms which touches a an atoms.
Atomic packing factor :
It is also known as packing efficiency.It is the fraction of volume in a Crystal which is filled by constituent particles.It is always less than 1.Generally it is represented in the fraction.
Ex:
Lets take FCC cubic cell
Coordination number = 12 .
Atomic packing factor = 74%
Answer:
The original length of the specimen 
Explanation:
Original diameter
= 30 mm
Final diameter
= 30.04 mm
Change in diameter Δd = 0.04 mm
Final length
= 105.20 mm
Elastic modulus E = 65.5 G pa = 65.5 ×
M pa
Shear modulus G = 25.4 G pa = 25.4 ×
M pa
We know that the relation between the shear modulus & elastic modulus is given by



This is the value of possion's ratio.
We know that the possion's ratio is given by


0.00476

Final length
= 105.2 m
Original length


This is the original length of the specimen.
I say the answers is A but if you mean ventilation in the area of the room then answer B