This is true, this isn't a question, it's a fact.
Answer:
Volume
Explanation:
Density:
Density is equal to the mass of substance divided by its volume. In order to find the density of earth when mass is given we have to calculate its volume. The volume of earth is calculated by using the volume formula for sphere. i.e 4/3 π r³. we also require radius to find the volume and we know that
Diameter = 2 × radius
The diameter of earth equator is 12756.75 Km. So we calculate the radius by dividing the diameter by 2. Then by putting the value of radius in 4/3 π r³ we will get the volume and then we can calculate the density of earth.
Units:
SI unit of density is Kg/m3.
Other units are given below,
g/cm3, g/mL , kg/L
Formula:
D=m/v
D= density
m=mass
V=volume
Symbol:
The symbol used for density is called rho. It is represented by ρ. However letter D can also be used to represent the density.
<u>Answer:</u> Osmolarity of the sodium chloride solution is 18 Osmol/L.
<u>Explanation:</u>
Osmolarity is defined as the the concentration of the solution which is expressed as the total number of solution particles present in one liter of solvent.
We are given the molarity of the solution which is 3mol/L and to convert it into osmolarity, we will multiply the number of osmoles that are produced by the solute.
Osmole is defined as the particles that contribute to the osmotic pressure of a solution.
The solute given here is sodium chloride (NaCl). Number of osmoles can be determined by the dissociation of this solvent into ions.
The equation given by the dissociation of NaCl:

1 mole of sodium chloride produces 2 moles of ions.
So, 3 moles of sodium chloride will produce = (3 × 2) = 6 moles of ions.
Hence, osmolarity of the sodium chloride solution will be 
I believe it is C, as helium is one of the lightest noble gases making the particles move faster.