Answer:
a)22.2°C after adding magnesium
b)17.3°C before adding magnesium
c) 4.9 is change
Answer:
The coefficient of thermal expansion α is

The coefficient of compressibility

Now considering 
From equation (1) we have that

From ideal equation

So

=> 
=> 
Explanation:
From the question we are told that
The coefficient of thermal expansion is 
The coefficient of compressibility is 
Generally the ideal gas is mathematically represented as

=> 
differentiating both side with respect to T at constant P

substituting the equation above into 


Recall from ideal gas equation 
So

Now differentiate equation (1) above with respect to P at constant T

substituting the above equation into equation of 


Recall from ideal gas equation that

So

Now considering 
From equation (1) we have that

From ideal equation

So

=> 
=> 
True!
For example:
The atomic mass of carbon is 12.011 (i think) and the weight of carbon is 12. But with C13 and C14 being a little higher, it makes the average higher. Random fact: C14 is used for carbon dating.