Answer:
The density of the ideal gas is directly proportional to its molar mass.
Explanation:
Density is a scalar quantity that is denoted by the symbol ρ (rho). It is defined as the ratio of the mass (m) of the given sample and the total volume (V) of the sample.
......equation (1)
According to the ideal gas law for ideal gas:
......equation (2)
Here, V is the volume of gas, P is the pressure of gas, T is the absolute temperature, R is Gas constant and n is the number of moles of gas
As we know,
The number of moles: 
where m is the given mass of gas and M is the molar mass of the gas
So equation (2) can be written as:

⇒ 
⇒
......equation (3)
Now from equation (1) and (3), we get
⇒ Density of an ideal gas:
⇒ <em>Density of an ideal gas: ρ ∝ molar mass of gas: M</em>
<u>Therefore, the density of the ideal gas is directly proportional to its molar mass. </u>
The energy of the wave does not move through anything
Answer:
4) Van der waals forces
Explanation:
Krypton (Kr) belongs to the noble gas group and has fully filled valence orbitals. In the solid phase, Kr exists as a white solid with a face centered cubic structure.
Intermolecular forces of attraction from the strongest to the weakest include:
Ionic > hydrogen bonding > dipole-dipole > london dispersion
Kr is monoatomic and non-polar. When fully filled (stable) valence orbitals of 2 Kr atoms approach each other in close proximity they experience a repulsive force which prevents the formation of strong bonds. Thus, the only force of attraction in Kr is the long range weak Van Der Waals force also known as the london dispersion force.