A) 
The minimum speed of the electron occurs when the electron loses the maximum energy: this occurs when the electron excites the atom from 0.0 eV to 4.0 eV, because in this case the energy given to the atom is maximum.
The energy given by the electron to the atom is equal to the difference between the two energy levels:
This is equal to the kinetic energy lost by the electron:
where
m is the electron's mass
v is the final speed of the electron after the collision
is the speed of the electron before the collision
Solving for v, we find
B) 
The maximum speed of the electron occurs when the electron loses the minimum amount of energy: this occurs when the electron excites the atom from 3.0 eV to 4.0 eV, because in this case the energy given to the atom is minimum.
The energy given by the electron to the atom is equal to the difference between the two energy levels, so in this case we have:
And so, this time the final speed of the electron after the collision will be given by:
A scrap heap magnet can move Ferrous metals, so any metals containing Iron, stainless steel, steel etc.
And it cannot move anything that is not magnetic
(I hoped this helped ;) And good luck!)
B. The moon is located between the Sun and Earth
Answer:
The "2" tells us that there are 2 hydrogen atoms in this compound.
Explanation:
Answer:
In the air
Explanation:
There are three states of matter:
- Solids: in solids, the particles are tightly bond together by strong intermolecular forces, so they cannot move freely - they can only vibrate around their fixed position
- Liquids: in liquids, particles are more free to move, however there are still some intermolecular forces keeping them close to each other
- Gases: in gases, particles are completely free to move, as the intermolecular forces between them are negligible
For this reason, it is generally easier to compress/expand the volume of a gas with respect to the volume of a liquid.
In this problem, we are comparing water (which is a liquid) with air (which is a gas). From what we said above, this means that the change in volume is larger in the air rather than in the water.
