Answer:
Explanation:
To answer this question successfully, we need to remember that atoms are neutral species, since the number of protons, the positively charged particles, is equal to the number of electrons, the negatively charged particles. That said, we may firstly find an atom which has 3 electrons (and, as a result, 3 protons, as it should be neutral).
The number of protons is equal to the atomic number of an element. We firstly may have an atom with 3 protons and 3 electrons (atomic number of 3, this is Li).
Similarly, we may take the atomic number of 4, beryllium, and remove 1 electron from it. Upon removing an electron, it would become beryllium cation, 
.
We may use the same logic going forward and taking the atomic number of 5. This is boron. In this case, we need to remove 2 electrons to have a total of 3 electrons. Removal of 2 electrons would yield a +2-charged cation: 
.
Answer:
315.
Explanation:
Hello.
In this case, since the given number has five significant figures as the zero is to the right of the first nonzero digit (3), if it is required to report it with three significant figures, it is necessary to "cut" it at the first five without any rounding since the subsequent zero is less than five.
Thus the number turns out:
315
Best regards.
The number of moles in monochloro pentaborane (9) 
is 0.37056.
We know that ,
Number of moles = Given mass/ Molar mass
Given mass of monochloro pentaborane (9) is 20.1 g
The molar mass of monochloro pentaborane (9) is
= 
= 
= 54.241
Thus number of moles = 20.1/54.241
= 0.37056
To know more about mole concept
brainly.com/question/20483253
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First, you need to find:
One mole of
is equivalent to how many grams?
Well, for this you have to look up the periodic table. According to the periodic table:
The atomic mass of Calcium Ca = 40.078 g (See in group 2)
The atomic mass of <span>Chlorine Cl = 35.45 g (See in group 17)
</span>
As there are two atoms of Chlorine present in
, therefore, the atomic mass of
would be:
Atomic mass of
= Atomic mass of Ca + 2 * Atomic mass of Cl
Atomic mass of
= 40.078 + 2 * 35.45 = 110.978 g
Now,
110.978 g of
= 1 mole.
75.9 g of
=
= 0.6839 moles.
Hence,
The total number of moles in 75.9g of
= 0.6839 moles
According to <span>Avogadro's number,
1 mole = 1 * </span>
molecules
0.6839 moles = 0.6839 *
molecules =
molecules
Ans: Number of molecules in 75.9g of = molecules
-i
