Answer:
There was an improvement in accuracy. There was no change in precision.
Explanation:
<em>The average mass after recalibration is closer to the mass of the standard, </em>so the recalibration improved the accuracy<em> </em>(the measurement is closer to an accepted 'true' value).
The standard deviation did not change, so the precision (or how disperse the measurements are) was not affected.
In a sample of pure calcium fluoride of mass 15.0 g, 7.70 g of calcium is present. First convert the mass into number of moles as follows:
Here, m is mass and M is molar mass.
Molar mass of Ca is 40 g/mol, putting the values,
Similarly, molar mass of 
is 78.07 g/mol thus, number of moles will be:
.
Thus, 0.1921 mol of have 0.1925 mol of Ca, or 1 mole of will have approximately 1 mole of Ca.
Now, mass of Ca needs to be calculated in 45.0 g of . Converting mass into number of moles first,
Thus, number of moles of Ca will also be 0.5764 mol, converting number of moles into mass,
Therefore, mass of Ca will be 23.06 g.
1. option B
2. ground state Fe : [Ar] 4s² 3d⁶
<h3>
Further explanation</h3>
Aufbau rule
<em>Electrons occupy orbitals of the lowest energy level</em>
Charging electrons in the sub-shell uses the following sequence:
1s², 2s², 2p⁶, 3s², 3p⁶, 4s², 3d¹⁰, 4p⁶, 5s², 4d¹⁰, 5p⁶, 6s², etc.
So the correct choice of answer is B.
Ground state is the state of electrons filling skins with the lowest energy levels.
Excited state is the state of electrons which occupy a higher energy level
The atomic number of Fe = 26, so electrons=26
Ground state configuration of Fe : [Ar] 4s² 3d⁶ or
1s², 2s², 2p⁶, 3s², 3p⁶, 4s², 3d⁶
