The atomic mass of an element is the average mass of the atoms of an element measured in atomic mass unit (amu, also known as daltons, D). The atomic mass is a weighted average of all of the isotopes of that element, in which the mass of each isotope is multiplied by the abundance of that particular isotope. (Atomic mass is also referred to as atomic weight, but the term "mass" is more accurate.)

So, your answer to this problem is
c = 4.
Answer:

1) 
2) 
We can find the individual probabilities and we got:



And the sum of the 3 values 0.6923+0.2307+0.0770= 1 so then we satisfy all the conditions and we can conclude that f(x) is a probability distribution.



Step-by-step explanation:
For this case we have the following density function:

In order to satisfty that this function is a probability mass function we need to check two conditions:
1) 
2) 
We can find the individual probabilities and we got:



And the sum of the 3 values 0.6923+0.2307+0.0770= 1 so then we satisfy all the conditions and we can conclude that f(x) is a probability distribution.
And if we want to find the following probabilities:


