I think the answer you are looking for is D.
Hope this helps!!! :D
Answer:

Explanation:
Hello!
In this case, we can divide the problem in two steps:
1. Dilution to 278 mL: here, the initial concentration and volume are 1.20 M and 52.0 mL respectively, and a final volume of 278 mL, it means that the moles remain the same so we can write:

So we solve for C2:

2. Now, since 111 mL of water is added, we compute the final volume, V3:

So, the final concentration of the 139 mL portion is:

Best regards!
Answer:
The answer would be C. Number of protons in the atom.
Explanation:
On the periodic table, you see the element, with a big number at top, and a small number below the element name/abbreviation.
The big number is the amount of protons of the atom, which define each atom. The smaller number represents the atomic mass of the atom.
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Answer:
Average atomic mass = 51.9963 amu
Explanation:
Given data:
Abundance of Cr⁵⁰ with atomic mass= 4.34%
, 49.9460 amu
Abundance of Cr⁵² with atomic mass = 83.79%, 51.9405 amu
Abundance of Cr⁵³ with atomic mass =9.50%, 52.9407 amu
Abundance of Cr⁵⁴ with atomic mass = 2.37%, 53.9389 amu
Average atomic mass = 51.9963 amu
Solution:
Average atomic mass = (abundance of 1st isotope × its atomic mass) +(abundance of 2nd isotope × its atomic mass +....n) / 100
Average atomic mass = (4.34×49.9460)+(83.79×51.9405) +(9.50×52.9407)+ (2.37×53.9389) / 100
Average atomic mass = 216.7656 + 4352.0945 + 502.9367 +127.8352 / 100
Average atomic mass = 5199.632 / 100
Average atomic mass = 51.9963 amu