Answer:
Option C. 1
Explanation:
Step 1:
Determination of the Neutron of both isotopes. This is illustrated below. 
For isotope y xA:
Mass number = y
Atomic number = x
Neutron =..? 
Atomic number = proton number = x
Mass number = Proton + Neutron 
y = x + Neutron 
Rearrange 
Neutron = y – x
For isotope (y + 1) xA:
Mass number = y + 1
Atomic number = x
Neutron =.? 
Atomic number = proton number = x
Mass number = Proton + Neutron 
y + 1 = x + Neutron 
Rearrange 
Neutron = y + 1 – x
Step 2:
Determination of the difference between the neutron number of both isotopes. This is illustrated below:
For isotope y xA:
Neutron number = y – x
For isotope (y + 1) xA:
Neutron number = y + 1 – x
Difference in neutron number
=> (y + 1 – x) – (y – x) 
=> y + 1 – x – y + x
Rearrange
=> y – y + 1 – x + x
=> 1
Therefore, the difference in the neutron number of both isotopes is 1
 
        
             
        
        
        
The mass number of this particular element is 37
An element with 17 protons will ALWAYS be chlorine.
The mass number is found by adding the element’s protons and neutrons.
protons+neutrons=mass number 
Here is the math if needed,
17+20=37
Therefore the mass number is 37
I hope this helped!
        
             
        
        
        
The following are scientific observations which led to development and changes of periodic table: Dmitri Mendeleev is the first periodic table organized 63 known element according to its properties, organized into rows and columns and inscribed name, mass and chemical properties on each element. Julius Lothar Meyer who independently worked in Germany with Ernest Rutherford. They experimented with 38 metals and found out that the positive charge of each element nucleus increased by one from element to element and organized the periodic table that tip to modern explanation of atomic number and the recognition of atomic number was the basis for organization of periodic table.
        
             
        
        
        
Answer:
When heat is added to a substance, the molecules and atoms vibrate faster. As atoms vibrate faster, the space between atoms increases. The motion and spacing of the particles determines the state of matter of the substance. The end result of increased molecular motion is that the object expands and takes up more space.
hope this helps!!!!!!