An orbital that penetrates into the region occupied by core electrons is less shielded from nuclear charge than an orbital that does not penetrate and therefore has a lower energy.
Explanation:
The only true statement from the given options is that "an orbital that penetrates into the region occupied by core electrons is less shielded from nuclear charge than an orbital that does not penetrate and therefore has a lower energy." Inner orbitals which are also known to contain core electrons feels the bulk of the nuclear pull on them compared to the outermost orbitals containing the valence electrons.
- The nuclear pull is the effect of the nucleus pulling and attracting the electrons in orbitals.
- This pull is stronger for inner orbitals and weak on the outer ones.
- The outer orbitals are said to be well shielded from the pull of the nuclear charge.
- Also, based on the quantum theory, electrons in the outer orbitals have higher energies because they occupy orbitals at having higher energy value.
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Answer: 
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Explanation:
The order of boiling point depends upon the type of interactions present between the molecules.
Potassium fluoride (KF) is an ionic compound and the opposite ions are held together by strong electrostatic forces.
is a covalent compound and the molecules are held together by weak van der Waals' forces.
Formaldehyde is a polar compound due to presence of polar carbonyl group. Hence dipole-dipole force is present between formaldehyde molecules.
Thus the decreasing order of boiling point is:
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Preparing 15 mg/gl working standard solution from a 20 mg/dl stock solution will require the application of the dilution principle.
Recalling the principle:
initial volume x initial molarity = final volume x final molarity
Since we were not given any volume to work with, we can as well just take an arbitrary volume to be prepared. Let's assume that the stock solution is 10 mL and we want to prepare 15 mg/gl from it:
Applying the dilution principle:
10 x 20 = final volume x 15
final volume = 200/15
= 13.33 mL
This means that in order to prepare 13.33 mL, 15 mg/l working standard solution from 10 ml, 20 mg/dl stock solution, 3.33 mL of the diluent must be added to the stock solution.
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The most common pH indicator used in Simmons Citrate Agar is Bromthymol Blue (BTB)
Simmons Citrate Agar is a selective and differential medium used for the detection and differentiation of Enterobacteriaceae (gram-negative bacteria).
The medium contains sodium citrate as the sole carbon source, which is used to differentiate organisms based on their ability to utilize citrate as a sole carbon source.
The medium also contains pH indicators that change color based on the pH of the medium. The most common pH indicator used in Simmons Citrate Agar is Bromthymol Blue (BTB).
BTB is a pH indicator that turns yellow in acidic conditions and blue in basic conditions. As the bacteria metabolize the citrate in the medium, they produce acids, which cause the medium to become acidic.
This change in pH is detected by the BTB, which changes color from blue to yellow. The yellow coloration of the medium is an indication that the organism is utilizing citrate as a sole carbon source.
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