Explanation​:
There is an inverse relationship between frequency and wavelength. If the wavelength is doubled, the frequency will decrease by half. Therefore, Choices A, C, and D are all incorrect.

Explanation:
Seawater is a mixture of water and salts. Sucrose, distilled water, and sodium chloride are all examples of compounds.

Explanation:​
The student must understand the concepts behind an ideal gas which assumes negligent volume and insignificant attractive forces between atoms or molecules.
As the molar mass of a chemical species increases, the attractive forces between particles also increase. This causes a deviation from the ideal gas model as the relative molecular mass increases.
This question is categorized as medium difficulty because the student must apply logic to the definition of an ideal gas.

Explanation​:
1 mole is the number of H2​ molecules in 2.02 g of H2​. Choices A, B, and C all conform to the definition of a mole.

Explanation:
The s orbital has a spherical shape. In terms of energy, s has the lowest, followed by p and d orbital. Thus, Choices A, B, and D are all incorrect.

Explanation​:
The student must correctly understand the process of paper chromatography. Components of a mixture can be successfully separated using paper chromatography only if the components are soluble in the mobile phase (the solvent). The components of the mixture can be liquids or solids when pure.
This question is categorized as medium because the student must understand that solubility in the mobile phase is essential for a successful separation using paper chromatography. Beyond that, there are no calculations or other facts to recall.

Explanation:
The student must first understand that each component of the mixture will result in one spot on the paper chromatogram. If the recrystallization was successful, then the purified dye should only have one dot.
Therefore, answer choice B is incorrect since the sample contains more than one component after recrystallization.
Answer choice C indicates that the dye is no longer in the sample, and answer choice D indicates the contaminant was not successfully separated from the dye. So the paper chromatogram is unable to identify any impurities that are still present.
In answer choice A, before recrystallization, shows two components (the dye and contaminant), and after, there is only one component showing successful recrystallization.
This question is categorized as medium since the student must understand the premise and purpose of paper chromatography and apply it to experimental results.

Explanation:
For p, $l$ is equal to 1. The number of electrons in a given subshell can be calculated using the formula: 2(2 l+1)=2((2)(1)+1)=6 electrons.

The p subshell holds 3 orbitals. Each orbital can fit 2 electrons. Therefore, p subshell holds 6 electrons.

Explanation​:
The lines converge as energy levels increase (increased distance from the nucleus).
Higher energies result in higher frequencies.

Explanation:
Explanation: Selenium's electron configuration is 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^10 4p^4. The three $2p$ and three $3p$ orbitals are fully occupied, along with one 4p orbital.

Explanation​:
Ions do not have the same numbers of protons and electrons. Only species B and C do not have the same number of protons and electrons, so the correct answer is B.

Explanation:​
The $\mathrm{Mn}$ atom and Mn^2+ ion have the following orbital diagrams:

The valence electrons and the two lost in the 2+ ion are the $4s$ electrons so the unpaired electrons remain 5.

Explanation​:
Relative atomic mass of Br=(0.5069)(78.92)+(0.4931)(80.92)=79. The rest of the choices are incorrect relative atomic masses of bromine.

Alternative Method​:

79Br atomic mass can be rounded up to 79

81Br atomic mass can be rounded up to 81

Since the relative abundance of both isotopes is about 50% each, the relative atomic mass of Bromine should be close to 80. Choice D corresponds to that estimation.

Explanation:
The graph of P vs T shows a linear graph (straight line passing through the origin) that rises upward. This graph shows that P is directly proportional to the absolute temperature. As the absolute temperature increases, the pressure of the gas also increases.

Explanation​:
Choice B is incorrect because electrons are not located in the nucleus. Choice C is incorrect because an orbital diagram is just a representation of electrons in an orbital. Choice D is incorrect because electrons can be found in orbit (a specific energy level around the positively charged nucleus) but the probability is relatively low. Choice A is the correct answer: orbitals are areas/ regions in space where the probability of finding an electron is very high.

Explanation​:
The student must first recall that the component with the greatest affinity for the mobile phase will travel the furthest in paper chromatography. In this case, spot #2 is the furthest from the starting line, so it has the greatest affinity for the mobile phase.
In paper chromatography, the mobile phase is always the solvent (water, in this case), while the stationary phase is the paper.
This question is categorized as easy because the student must only recall basic definitions and concepts for paper chromatography.

Explanation:​
Electrons fill sublevels according to the Aufbau Principle shown below: 

Following this order, $2p<4s<3d<4p$

Explanation​:
According to Aufbau’s principle, the arrangement of subshell in increasing energy is 1s 2s 2p 3s 3p 4s 3d 4p. Therefore, Choices A and B are both incorrect. Choice C is incorrect because 2d does not exist.

Explanation​:
Isotopes have the same number of protons but different numbers of neutrons.
Species A and B have the same number of protons but also the same number of neutrons so cannot be isotopes.
Species C is the only species in the table with 9 protons so cannot have an isotope with another species in the table.
This leaves species D and E which both have the same number of protons but a different number of neutrons. Therefore, the correct answer is D.

Explanation​:
At high pressures and very low temperatures, the inter-particle forces strengthen, spaces between particles decrease causing the deviation from ideal gas behaviour PV/nRT> 1