Pre AP Chemistry -2.2D Lewis Diagrams and Structural Isomerism- MCQ Exam Style Questions -New Syllabus 2025-2026

Pre AP Chemistry -2.2D Lewis Diagrams and Structural Isomerism- MCQ Exam Style Questions – New Syllabus 2025-2026

Pre AP Chemistry -2.2D Lewis Diagrams and Structural Isomerism- MCQ Exam Style Questions – Pre AP Chemistry – per latest Pre AP Chemistry Syllabus.

Pre AP Chemistry – MCQ Exam Style Questions- All Topics

Question

Which row gives the number of covalent bonds in one molecule of ammonia and in one molecule of hydrogen chloride?

	ammonia	hydrogen chloride
A	3	1
B	3	2
C	4	1
D	4	2

▶️ Answer/Explanation

Solution

Ans: A

Ammonia (NH₃) has 3 covalent bonds – one between nitrogen and each hydrogen atom. Nitrogen has 5 valence electrons and forms 3 single bonds, leaving one lone pair.

Hydrogen chloride (HCl) has just 1 covalent bond between the hydrogen and chlorine atoms. Hydrogen can only form one bond, and chlorine needs just one more electron to complete its outer shell.

Therefore, the correct combination is 3 bonds in ammonia and 1 bond in hydrogen chloride.

Question

Ammonia, $NH_3$, is a covalent molecule.
Which diagram shows the outer shell electron arrangement in a molecule of ammonia?

▶️ Answer/Explanation

Solution

Ans: C

Ammonia ($NH_3$) has a nitrogen atom with 5 valence electrons, forming 3 covalent bonds with hydrogen atoms (each contributes 1 electron). The nitrogen retains 1 lone pair of electrons. Diagram C correctly shows:
1. Three N-H bond pairs (shared electrons).
2. One lone pair on nitrogen.
The other diagrams either misplace electrons or incorrectly represent bonding.

Question

The electronic structures of atoms X and Y are shown.

X and Y form a covalent compound. What is its formula?

A) $XY_5$ B) $XY_3$ C) $XY$ D) $X_3Y$

▶️ Answer/Explanation

Solution

Ans: D

From the electronic structures:

Atom X has 1 valence electron (needs to lose 1 or share to stabilize).
Atom Y has 5 valence electrons (needs 3 more to complete its octet).

To form a stable covalent compound:

Each Y shares 3 of its electrons with 3 X atoms.
Each X shares its 1 electron with Y.

Thus, the formula is $X_3Y$, where Y achieves an octet by bonding with three X atoms.

Other options are incorrect because:

$XY_5$ would require X to share 5 electrons (impossible with only 1 valence electron).
$XY_3$ would leave Y with an incomplete octet (only 6 electrons).
$XY$ would not satisfy Y’s octet requirement (only 6 electrons total).

Question

The diagrams show the electron arrangements in the atoms of four elements.

Which element does not form a covalent bond?

▶️ Answer/Explanation

Solution

Ans: A

The element represented by A is lithium (Li), which has one valence electron. To achieve stability, lithium tends to lose this electron, forming a positive ion (Li⁺). This behavior is characteristic of ionic bonding, not covalent bonding.

In contrast, elements like B, C, and D (likely nonmetals such as oxygen or fluorine) share electrons to complete their valence shells, forming covalent bonds. Since Li does not share electrons but instead transfers them, it does not form covalent bonds.

Question

Which statement describes a homologous series?

A) a family of elements in the same group of the Periodic Table
B) a family of elements with similar chemical properties
C) a family of compounds with the same functional group
D) a family of compounds with similar physical properties

▶️ Answer/Explanation

Solution

Ans: C

A homologous series is a family of organic compounds that:

Have the same functional group
Show a gradual change in physical properties
Have similar chemical properties
Differ by a CH₂ unit in their molecular formulae

Key points:

Option A describes groups in the Periodic Table, not homologous series
Option B is partially correct but too vague – it’s about compounds, not elements
Option D is partially correct but not the complete definition
Option C is the most accurate as the functional group defines the series (e.g., alcohols, alkanes)

Examples of homologous series include alkanes (CH₄, C₂H₆, etc.) and alcohols (CH₃OH, C₂H₅OH, etc.).

Question

PVA is a polymer. The monomer has the structure shown.

To which homologous series does this compound belong?

▶️ Answer/Explanation

Solution

Ans: A

The monomer structure shows:
1. A hydroxyl (–OH) group, characteristic of alcohols.
2. A carbon-carbon double bond (C=C), characteristic of alkenes.
Thus, it belongs to both alcohol and alkene series, but the primary functional group (alcohol) takes precedence in classification. The homologous series is determined by the –OH group, making it an alcohol.

Question

Three statements about ammonia molecules and ammonium ions are given.

1. In aqueous solution, ammonia molecules form coordinate bonds with hydroxide ions.
2. Ammonium ions are Brønsted–Lowry acids.
3. The H–N–H bond angle is larger in the ammonium ion than in the ammonia molecule.

Which statements are correct?

A. 1 and 2 only B. 1 and 3 only C. 2 and 3 only D. 1, 2 and 3

▶️ Answer/Explanation

Solution

Ans: C

Statement 1: Incorrect. Ammonia ($NH_3$) forms coordinate bonds with $H^+$ ions (protons) to form ammonium ions ($NH_4^+$), not hydroxide ions ($OH^-$).

Statement 2: Correct. Ammonium ions ($NH_4^+$) can donate a proton ($H^+$), making them Brønsted–Lowry acids.

Statement 3: Correct. The $H-N-H$ bond angle in $NH_4^+$ (≈109.5°, tetrahedral) is larger than in $NH_3$ (≈107°, trigonal pyramidal) due to the absence of a lone pair in $NH_4^+$.

Thus, only statements 2 and 3 are correct, making C the correct answer.

Question

Kerosene is used as an aircraft fuel. Q is one of the molecules in kerosene and has the skeletal formula shown.

Other structural isomers of this molecule are also found in kerosene.
Which structure is a structural isomer of Q?

▶️Answer/Explanation

Ans:D

Question

Structural isomerism and stereoisomerism should be considered in answering this question.
Compound $\mathrm{J}$ is reacted with $\mathrm{KOH}$ dissolved in ethanol. Three isomeric alkenes with molecular formula $\mathrm{C}_4 \mathrm{H}_8$ are formed.
What is $\mathrm{J}$ ?

▶️Answer/Explanation

Ans:B

Question

In this question, alkenes and cyclic alkanes should be considered.
How many structural isomers of $C_4H_8$ are there?
A 3 B 4 C 5 D 6

Answer/Explanation

Ans: C

Question

Structural isomerism only should be considered when answering this question.

Molecule X contains three C=C double bonds. One mole of X is reacted with three moles of HBr.
The carbon skeleton is unchanged.

How many different products are formed?

A 3 B 4 C 6 D 8

Answer/Explanation

Answer B

Question

How many structural isomers are there of trichloropropane, C₃H₅Cl₃?
A 3 B 4 C 5 D 6

Answer/Explanation

Answer:

Question

Structural isomerism and stereoisomerism should be considered when answering this question. 2-bromopentane is heated with an excess of ethanolic sodium hydroxide.

How many different hydrocarbons are produced?
A 1 B 2 C 3 D 4

Answer/Explanation

Answer:

Question

Structural isomerism only should be considered when answering this question.

All the isomeric alcohols with the molecular formula C₅H₁₂O are added separately to warm alkaline aqueous iodine.

How many of the isomers give a yellow precipitate?
A 0 B 1 C 2 D 3

Answer/Explanation

Answer:

Question

Structural isomerism and stereoisomerism should be considered when answering this question.
3-methylhexan-3-ol reacts with hot, concentrated sulfuric acid to form several isomeric compounds with the molecular formula C₇H₁₄.

How many isomeric compounds could be formed in this reaction?
A 3 B 4 C 5 D 6

Answer/Explanation

Answer C

Question

A new jet fuel has been produced that is a mixture of different structural isomers of compound Q.

Which skeletal formula represents a structural isomer of Q?

Answer/Explanation

Answer C

Question

X has the molecular formula C₅H₁₂O. X has a branched carbon skeleton and a secondary alcohol functional group.

How many structural isomers fit this description of X?

A 1 B 2 C 3 D 4

Answer/Explanation

Answer A

Question

In 1869 Ladenburg suggested a structure for benzene, $C_{6}H_{6}$, in which one hydrogen atom is attached to each carbon atom.

A compound $C_{6}H_{4}Cl _{2}$ could be formed with the same carbon skeleton as the Ladenburg structure.
How many structural isomers would this compound have?
A 3 B 4 C 5 D 6

Answer/Explanation

Ans:D

Question

How many isomeric esters have the molecular formula $C_{4}H_{8}O_{2} $?
A 2 B 3 C 4 D 5

Answer/Explanation

Ans:C

Question

Considering only structural isomers, what is the number of alcohols of each type with the formula $C_{5}H_{12}O$?

Answer/Explanation

Ans:C

Question

Which dot-and-cross diagram is correct for $Al_2Cl_6$?

Answer/Explanation

Ans: B

Question

In which structure are three atoms bonded together in a straight line?
A poly(ethene), $-(-CH_2CH_2-)_n-$
B propane, $C_3H_8$
C silicon tetrachloride, $SiCl_4$
D sulfur hexafluoride, $SF_6$

Answer/Explanation

Ans: D

Question

Which molecules contain at least one unpaired electron?

1 NO
2 NO₂
3 NH₃

Answer/Explanation

Answer B

Question

In which species is there a lone pair of electrons?
A CH₃ B CH₃⁺ C CH₃^– D CH₄

Answer/Explanation

Answer C

Question

Which molecule contains six bonding electrons?
A $C_2H_4$ B $H_2S$ C $NCl_3$ D $SF_6$

Answer/Explanation

Ans: C

Question

In which species does the underlined atom have an incomplete outer shell?
A BF₃ B CH₃^– C F₂O D H₃O⁺

Answer/Explanation

Ans:

Pre AP Chemistry -2.2D Lewis Diagrams and Structural Isomerism- MCQ Exam Style Questions -New Syllabus 2025-2026