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>
Answer : The value of 
at this temperature is 66.7
Explanation : Given,
Pressure of 
at equilibrium = 0.348 atm
Pressure of 
at equilibrium = 0.441 atm
Pressure of 
at equilibrium = 10.24 atm
The balanced equilibrium reaction is,
The expression of equilibrium constant for the reaction will be:
Now put all the values in this expression, we get :
Therefore, the value of at this temperature is 66.7
Answer:
Chemistry is used in forensic science to uncover information from physical evidence.
Hope this helps
The charge of this atom would be -2
Answer:
Explanation:
Beta decay conserves the lepton number. In 
decay, the atomic number of the element increases which is accompanied by the release of an electron antineutrino, 
.
For example:-
The decay of silicon-32 is shown below as:-
