Answer:
Explanation:
An electron-donating heteroatom substituent at position-2 of a furan promotes regiospecific opening of the 7-oxa bridge of the Diels-Alder cycloadduct with hexafluoro-2-butyne, producing a 4-heterosubstituted 2,3-di(trifluoromethyl)phenol building block in a single step. The phenol and heteroatom substituent are easily transformed to the corresponding iodide or triflate that readily undergoes Heck, Suzuki, and Stille reactions to install a variety of substituents in high yields. This methodology provides a facile and general synthesis of 1,4-disubsituted 2, 3-di(trifluoromethyl)benzenes.
Answer:
The empirical formula is = 
Explanation:
Given that:- Mass of nickel = 2.241 g
Mass of the oxide formed = 2.852 g
Mass of the oxygen reacted = Mass of the oxide formed - Mass of nickel = 2.852 g - 2.241 g = 0.611 g
Molar mass of nickel = 58.6934 g/mol
Moles of nickel = 
= 0.03818 mol
Molar mass of oxygen = 15.999 g/mol
Moles of nickel = 
= 0.03818 mol
Taking the simplest ratio for Ni and O as:
0.03818 : 0.03818 = 1 : 1
<u>The empirical formula is =
</u>
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The nulear charge is the number of protons.
As the number of protons increases, the nuclear charge grows ant thhe pulling electrostatic force between them and electrons also grows, given that the electrostatic force is proportional to the magnitude of the charges.
As the number of electrons grows, they occupy outer shelss (farther from the nucleus). And the outer electrons will feel not only the atraction of the protons from the nucleus, but the repulsion of the inner electrons.
Then, we see that the increase of nuclear charge is opposed by the increase of core electrons, and the outer (valence) electrons are not so tied to the nucleus as the core electrons are.
This is called shielding effect. A way to quantify the shielding effect is through the effective nuclear charge which is the number of protons (Z) less the number of core electrons.
The more the number of core shells the greater the shielding effect experience by electros in the outermost shells.
The shielding effect, explains why the valence eletrons are more easily removed from the atom than core electrons, and also explains some trends of the periodic table: variationof the size of the atoms in a row, the greater the shielding efect, the less the atraction force felt by the outermos electron, the farther they are and the larger the atom.
The Answer for this question is : A
1 & 2
