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:
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​:
One of the laws of gases states that, for a fixed amount of gas held at a constant temperature, the volume of a gas is inversely proportional to its pressure.

Explanation:
To answer this question, the student must understand the properties of the mixture's components.
The wood chips would not dissolve in the water, so they are filtered out first. This will leave the sodium chloride dissolved in the water. The water can be evaporated to remove the water (to isolate the salt).
Paper chromatography would be ineffective in this scenario as it is used for separating substances such as dyes, pigments, and proteins.
This question is categorized as medium complexity because the student must understand the properties of matter and separation techniques.

Explanation​:
The atomic number of sodium is 11. The atom loses one electron to become a stable ion with a charge of 1+ (10 electrons).
Choice A is incorrect because it shows the electron configuration of a sodium atom, not sodium ion. Choice B is incorrect because it shows an increase instead of a decrease by 1 electron.
Choice D is incorrect because of 2s^1.
Choice C is the correct answer. Ne has an atomic number 10. In a neutral atom, the number of electrons is equal to the number of protons. Therefore, Ne has 10 electrons in its atom. Sodium ion has 10 electrons too.

Explanation:

Isotopes with fewer neutrons will have a lower density

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:
An insoluble solid can be separated from a liquid by means of filtration. Distillation is used to separate homogeneous liquid mixtures (solid soluble in a liquid or two miscible liquids) with different boiling points. Sublimation is a technique for separating mixtures with volatile components that can undergo sublimation. Crystallisation is a separation technique that uses solubility properties to separate a solid from a solution.

Explanation:
Liquids have an indefinite shape (take the shape of the container) but have a definite volume. Choice A describes solids. Choices B and D describe the characteristics of gases.

Explanation​:
Vanadium has an atomic number of 23 therefore statement I is true. It also has a mass number of 51, therefore statement II is also true as nucleons include both protons and neutrons. Statement III is false as the closest noble gas is Ar, not Ne. The correct condensed electron configuration would be [Ar]4s23d^3. Therefore, the correct answer is A.

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

Explanation:

Electrons have negligible mass.

Explanation:
The shortest wavelength corresponds to a higher frequency and therefore a higher energy transition. The 5p to $1s$ represents the largest energy drop and therefore would produce the shortest wavelength.

Explanation​:
The number of arrows denotes the number of electrons the atom has. The orbital diagram shown here has 8 arrows which tells you that there are 8 electrons.
Choice A is not correct because C has only 6 electrons.
Choice D is also not correct because F has 9 electrons.
Choice C is incorrect as N has 7 electrons.
Among the choices, oxygen in its neutral form has 8 electrons. Hence, choice B is the correct answer.

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:
Second ionization energy is the energy required to remove one mole of electrons from one mole of singly positive gaseous ions.

Explanation​:

Isotopes are atoms of the same element with different numbers of neutrons that differ only in terms of their physical properties.

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 electron configuration for S is 1s2 2s2 2p6 3s2 3p4, whereas for $\mathrm{P}$, it is 1s2 2s2 2p6 3s2 3p3.
Due to the increased stability of P’s half-filled p-shell, more energy is required to remove an electron from a $\mathrm{P}$ atom than an $\mathrm{S}$ atom. The electron-electron repulsion in Sulfur makes it easier to remove the first electron.
First ionization energy increases across a period (due to a decrease in atomic radii and an increase in nuclear charge). In period 3, Na is the first element, and Ar is the last to the right.

Explanation:​
Condensation (gas to liquid) requires making bonds and therefore, releases energy. Sublimation (solid to gas) requires breaking bonds and therefore absorbs energy.

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