Danger, or some people look at it as love
In a physical change the appearance or form of the matter changes but the kind of matter in the substance does not. However in a chemical change, the kind of matter changes and at least one new substance with new properties is formed. The distinction between physical and chemical change is not clear cut.
When an electron moves from a higher energy shell to a lower one, energy in the form of light, more specifically a wavelength of a photon is released.
A.
Elements in the same group have similar properties.
B.
The similarity in their properties arises from the fact that they have an equal number of valence shell electrons.
C.
Fluorine, Chlorine, Bromine
Answer:

Explanation:
Step 1. Identify the Group that contains X
We look at the consecutive ionization energies and hunt for a big jump between them

We see a big jump between n = 2 and n = 3. This indicates that X has two valence electrons.
We can easily remove two electrons, but the third electron requires much more energy. That electron must be in the stable, filled, inner core.
So, X is in Group 2 and P is in Group 15.
Step 2. Identify the Compound
X can lose two valence electrons to reach a stable octet, and P can do the same by gaining three electrons.
We must have 3 X atoms for every 2 P atoms.
The formula of the compound is
.