Explanation:

The mass number is the sum of the number of protons and neutrons. For a neutral atom, the number of electrons is equal to the number of protons

Explanation:
Add $273$ to the temperature in Celsius to convert it to Kelvin. −185∘C+273=88 K. The rest of the choices are incorrect.

Explanation:​
The student must understand that gases deviate from an ideal gas when the temperature is low and when the pressure is high.
At low temperatures, the particles move slower and thus are able to form more intermolecular forces.
At high pressure the particles are closer together, also allowing for more plentiful attractive forces.
In both of these cases, intermolecular forces of attraction cannot be assumed to be negligible and so the gas under those conditions is no longer considered an ideal gas.
This question is categorized as medium because the student needs to carefully consider the answer choices. A pressure of 1 $atm$ is the same as 100 kPa. Likewise, 298 $K$ is the same as 25∘C. A pressure of 2 $atm$, while higher, is not high enough to drastically increase attractive forces. A pressure of 200 $atm$ would be consistent with the pressure in a compressed gas cylinder when the gas is in liquid form, and is therefore not behaving as an ideal gas.

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​:
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​:

N = n x NA​ = (4.80)(6.02 $\times$ 10^$)$ = 2.89 $\times$ 10^24 molecules of glucose

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

Following this order, $2p<4s<3d<4p$

Explanation:
Choice A is the correct answer because it satisfies Aufbau's principle and the number of electrons in the electron configuration aligns with the same number of electrons in the orbital diagram.

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

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:
Choice A is incorrect because the orbital diagram does not satisfy Hund's rule wherein all orbitals must be singly occupied before pairing.
Choice B is incorrect because Pauli's Exclusion principle is not obeyed by having two electrons with the same spin in one orbital.
Choice C is correct because, according to Hund's rule, the orbitals must be half-filled first before pairing, and the paired orbital must have electrons in an opposite spin.
Choice D is incorrect because the 2s orbital must be filled first before filling the 2p orbital, as illustrated by Aufbau's Principle.

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:
Cu has the electron configuration [Ar] 4s13d10 (a full d-subshell is more stable). The $4s$ electron is lost in the first ionization followed by a $3d$ electron.

Explanation​:
The empirical formula shows the simplest whole-number ratio of elements in a compound. The empirical formula can sometimes be the same as the molecular formula. Choices A, B, and D are all false statements.

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​:
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 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 atomic number is the number of protons. The mass number is the sum of the number of protons and neutrons. For a neutral atom, the number of electrons is equal to the number of protons.

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​:
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.