<span>What is the atomic number of the first element to start filling an "f" sub-level?
the answer is 58.
I hope this helps :)</span>
Your answer is x= 1/2, this is because to get the x alone you need to move the 2 so you divide 2x by to and you have to do the same to the other side so 1/2, and you get x=1/2
The atomic mass unit is presently based on assigning an exact integral mass (in amu) to an isotope of carbon.
<h3>What is the atomic mass?</h3>
The atomic mass is a measurement used in physics and chemistry to denote the average atomic mass of a given element which is measured in the atomic mass unit or amu.
In conclusion, the atomic mass unit is presently based on assigning an exact integral mass (in amu) to an isotope of carbon.
Learn more about the atomic mass here:
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Answer: 
Explanation:
Lattice energy : It is defined energy released when ions combine together in a gaseous phase to form a compound. it is energy possessed by the crystal lattice of a compound. Denoted by symbol
.
, energy is absorbed while forming of the lattice
, energy is release while forming of the lattice

One mole of sodium ion when combines with one mole chloride ion release 786 kJ of energy.