Answer:- The natural abundance of 
is 0.478 or 47.8% and 
is 0.522 or 52.2% .
Solution:- Average atomic mass of an element is calculated from the atomic masses of it's isotopes and their abundances using the formula:
Average atomic mass = mass of first isotope(abundance) + mass of second isotope(abundance)
We have been given with atomic masses for and as 150.919860 and 152.921243 amu, respectively. Average atomic mass of Eu is 151.964 amu.
Sum of natural abundances of isotopes of an element is always 1. If we assume the abundance of as n then the abundance of would be 1-n .
Let's plug in the values in the formula:
151.964=150.919860n+152.921243-152.921243n
on keeping similar terms on same side:
negative sign is on both sides so it is canceled:
The abundance of is 0.478 which is 47.8%.
The abundance of is = 
= 0.522 which is 52.2%
Hence, the natural abundance of is 0.478 or 47.8% and is 0.522 or 52.2% .
Answer:
I'm pretty sure it's A. BRUSH
Explanation:
If I'm wrong let ne know please
They can be separated by both means as they are only mixtures. (Two or more substances mixed together, and can be separated.)
Go to the Data tab > Sort & Filter group, and click Clear.
Go to the Home tab > Editing group, and click Sort & Filter > Clear.
6.060 has 4 significant figures including the zero after the decimal and the zero between non-zeros. 60.6 has 3 significant figures while 606 has also 3 significant figures. 60600 has 3 significant figures. Thus, the number with the greatest number of significant figures is 6.060.
