<u>Answer:</u> The density of liquid is 
<u>Explanation:</u>
We are given:
Mass of cylinder,  = 65.1 g
 = 65.1 g
Mass of liquid and cylinder combined, M = 120.5 g
Mass of liquid,  =
 = 
To calculate density of a substance, we use the equation:

We are given:
Mass of liquid = 55.4 g
Volume of liquid = 49.3 mL =  (Conversion factor:
    (Conversion factor:   )
 )
Putting values in above equation, we get:

Hence, the density of liquid is 
 
        
             
        
        
        
Answer:
A. there is an isotope of lanthanum with an atomic mass of 138.9
Explanation:
By knowing the different atomic masses of both Lanthanum atoms, we can not tell anything about their occurence in nature. Therefore, all the last three options are incorrect. Because, the atomic mass does not tell anything about the availability or natural abundance of an element.
Now, the isotopes of an element are those elements, which have same number of electrons and protons as the original element, but different number of neutrons. Therefore, they have same atomic number but, different atomic weight or atomic masses.
Hence, by looking at an elements having same atomic number, but different atomic masses, we can identify them as isotopes.
Thus, the correct option is:
<u>A. there is an isotope of lanthanum with an atomic mass of 138.9.</u>
 
        
             
        
        
        
Neutralization reaction is the reaction between acid and base.
There the neutralization reaction is:
HBr + LiOH ----------> LiBr + H2O.
Hope this helps!
        
                    
             
        
        
        
Carbon is 12 grams per mole
        
             
        
        
        
A- Change the phase of the matter