Explanation​:
The number of shells and therefore the shielding effect is the same for all of these species.
As the number of protons decreases, the attraction between the nucleus and electrons decreases, resulting in a smaller radius.
K^+ has the most protons (19), whereas S^2− has the least (16).

Explanation:​
First ionization energy is defined as the energy required to remove one mole of electrons from one mole gaseous atoms.

Explanation​:
The molecular formula of pentan-2-one is C5H10O

There are 5 C atoms and 10 H atoms, so the combustion produces 5115​ = 5 moles of CO2​ and 102210​ = 5 moles of H2O per mole of pentan-2-one. The value of b is therefore 5.0.

There are $15$ O atoms on the right-hand side of the equation but only 1 O atom in petan-2-one, so the compound must react with (15−1)/2​ = 7 moles of O2​. The value of a is therefore 7.0.

Explanation​:
Recall that the functional group is carboxyl and the class or series is carboxylic acid.

Explanation:​
The 6 protons in the nucleus of carbon will exert a stronger attractive force on the second energy level electrons than the 5 protons of boron.
Increasing electron affinity from left to right across a period.

Explanation​:
Amides have a C=O and C−N on the same central carbon atom.

Explanation:​
Group 17 melting points increase down the group due to increased strength in intermolecular forces. The molecular structures of each element are held together by London (dispersion) forces. These increase with the number of electrons in the molecule. Therefore statement I is not true, but III is.
Group 1 melting points decrease down a group due to decreasing metallic bond strength (with increase of atomic radius), therefore statement II is also true.

Explanation:​
Across the same period, metals have lower ionization energies than non-metals due to lower nuclear charges with the same number of shells (shielding effect).

Explanation​:
First ionization energy decreases down a group due to increased shielding (number of shells). Beryllium must therefore have a higher first IE than magnesium. And similarly, oxygen higher than sulfur.
First ionization energy increases across a period due to increased nuclear charge for the same number of shells. Hence, oxygen has higher first IE than beryllium.

Explanation​:
A tertiary amine is when three carbon groups are attached to the amine.

Explanation:​
The oxidation state of X in choices A, B, and C is +3. The oxidation state of X in choice D is +6.

Explanation:​
The air is naturally composed of 0.04% carbon dioxide, which dissolves in water to form the weak carbonic acid

Explanation​:
Increasing atomic radius results in a weaker electrostatic force of attraction between the nucleus and electrons in the covalent bond. An increased number of shells down the group increases the shielding between the nucleus and electrons in the covalent bond.

Explanation:
Ethers contain C−O single bonds $\text{not}$ the $\mathrm{C}=\mathrm{O}$ carbonyl group.

Explanation:​

Elements in the same group (column) of the periodic table have the same number of outer shell (valence) electrons, represented by the group number; the number of electron shells increases down the group. Elements in the same row (period) have the same number of electron shells (or principal quantum number), equal to the period number; the number of valence electrons increases across the period. This question is moderately difficult as the student must recall multiple pieces of information and correctly interpret a schematic illustration of the periodic table.

Explanation:​

Lithium is in group 1 and so forms Li+ ions. The formula of the nitride ion is N^3−as nitrogen is in group 15. For the positive and negative charges to cancel out, three Li+ ions are needed for each N^3− ion.

Explanation:​
Group 2 metal oxides produce alkaline metallic hydroxides when dissolved in water.

Explanation:​
Choices III and IV are ethene and ethyne with a double bond and a triple bond, respectively. They belong to the classes of alkenes and alkynes, which can be deduced by the general formulae, CnH2n​ and CnH2n−2 .
Choice I is the alkane methane, and choice II is a halogenoalkane (chloromethane).

Explanation:

The group of an element is determined by its atomic number, which is found in the lower left corner of the element symbol. Although this conflicts with the representation in the data booklet, students should be able to differentiate between the mass and atomic number based on their relative size. The elements represented by options A, B, C and D are calcium (an alkaline earth metal), iron (a transition metal), gallium (a poor / p block metal) and rubidium (an alkali metal), respectively. This question is moderately difficult as the student must identify the correct value from the given symbol and relate it to the position of an element in the periodic table.

Explanation​:
Saturated compounds contain only single bonds.
Butyne is an alkyne, and so, has a triple bond.

Explanation:​
Na^+, Ne, O^2−have 10 electrons in two energy levels with 11, 10, and 8 protons respectively. The increased number of protons has a greater pull on the 10 electrons and reduces the radius.
Ca^2+ has 18 electrons in 3 energy levels and is therefore, the largest.

Explanation:​
Statement III is not correct as physical properties, including melting point and metallic character, change dramatically across a period due to changes in nuclear charge for the same number of shells.
Elements in the periodic table are arranged in increased atomic number.
Anions are atoms that have gained electrons. This will increase the electron-electron repulsion in the outermost shell, and will cause the electrons to move further apart. Therefore, the radius of the outershell will increase.

Explanation​:
Statement II is incorrect as acids produce solutions with $\mathrm{pH}$ lower than 7.

Explanation:​

The names of the labelled groups are covered explicitly in the syllabus.