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>
<span>The normal dividing line for soluble/not soluble is 0.1 M.
If a substance, as a saturated solution at room temp and pressure, cannot form a solution concentration of 0.1 M, then it is considered insoluble.
The 0.1 M figure was selected because _most_ substances are either well above that value or well below. Some substances (calcium hydroxide is one? not sure) come close to the 0.1 M dividing line but there are only a very few.</span><span>
but most likely it wont mix</span>
Answer:
33.33 h
Explanation:
You know that
1 h = 60 min
If you divide both sides by 60 min, you get the conversion factor: 1 h/60 min = 1.
If you divide both sides by 1 h, you get the conversion factor: 1 = 60 min/1 h.
Both are conversion factors because they both equal one and multiplying a measurement by one does not change its value.
You choose the conversion factor that gives you the correct dimensions for your answer. It must have the correct dimensions on top (in the numerator),
Thus, to convert 2000 min to hours, you use the conversion factor with “h” on the top.
