Correct answer: A

The correct answer is It can form four covalent bonds and bond to itself in chains and rings.

1. Identify the organic chemistry concept: Determine whether the question concerns carbon structure, hydrocarbons, nomenclature, functional groups, reactions, polymers, or laboratory analysis.
2. Apply the structural principle: Carbon’s tetravalence and ability to form stable carbon–carbon bonds create enormous structural diversity.
3. Connect structure and reactivity: The correct answer is It can form four covalent bonds and bond to itself in chains and rings.

Correct answer: B

The correct answer is A hydrocarbon containing only single carbon–carbon bonds.

1. Identify the organic chemistry concept: Determine whether the question concerns carbon structure, hydrocarbons, nomenclature, functional groups, reactions, polymers, or laboratory analysis.
2. Apply the structural principle: Saturated hydrocarbons have the maximum number of hydrogens for their carbon framework and no multiple carbon–carbon bonds.
3. Connect structure and reactivity: The correct answer is A hydrocarbon containing only single carbon–carbon bonds.

Correct answer: C

The correct answer is $C_nH_{2n+2}$.

1. Identify the organic chemistry concept: Determine whether the question concerns carbon structure, hydrocarbons, nomenclature, functional groups, reactions, polymers, or laboratory analysis.
2. Apply the structural principle: Acyclic alkanes contain only single bonds and follow the formula (C_nH_{2n+2}).
3. Connect structure and reactivity: The correct answer is $C_nH_{2n+2}$.

Correct answer: D

The correct answer is An alkene contains at least one carbon–carbon double bond.

1. Identify the organic chemistry concept: Determine whether the question concerns carbon structure, hydrocarbons, nomenclature, functional groups, reactions, polymers, or laboratory analysis.
2. Apply the structural principle: The carbon–carbon double bond makes an alkene unsaturated and changes its geometry and reactivity.
3. Connect structure and reactivity: The correct answer is An alkene contains at least one carbon–carbon double bond.

Correct answer: A

The correct answer is It contains at least one carbon–carbon triple bond.

1. Identify the organic chemistry concept: Determine whether the question concerns carbon structure, hydrocarbons, nomenclature, functional groups, reactions, polymers, or laboratory analysis.
2. Apply the structural principle: Alkynes are unsaturated hydrocarbons with a carbon–carbon triple bond.
3. Connect structure and reactivity: The correct answer is It contains at least one carbon–carbon triple bond.

Correct answer: B

The correct answer is A specific group of atoms that gives an organic molecule characteristic reactivity.

1. Identify the organic chemistry concept: Determine whether the question concerns carbon structure, hydrocarbons, nomenclature, functional groups, reactions, polymers, or laboratory analysis.
2. Apply the structural principle: Functional groups such as hydroxyl, carbonyl, and amino groups strongly influence organic reactions and properties.
3. Connect structure and reactivity: The correct answer is A specific group of atoms that gives an organic molecule characteristic reactivity.

Correct answer: C

The correct answer is Compounds with the same molecular formula but different atom connectivity.

1. Identify the organic chemistry concept: Determine whether the question concerns carbon structure, hydrocarbons, nomenclature, functional groups, reactions, polymers, or laboratory analysis.
2. Apply the structural principle: Different connectivity can produce distinct physical properties and chemical behavior despite the same molecular formula.
3. Connect structure and reactivity: The correct answer is Compounds with the same molecular formula but different atom connectivity.

Correct answer: D

The correct answer is Its ring has a delocalized system of pi electrons that gives unusual stability.

1. Identify the organic chemistry concept: Determine whether the question concerns carbon structure, hydrocarbons, nomenclature, functional groups, reactions, polymers, or laboratory analysis.
2. Apply the structural principle: Benzene’s conjugated ring and delocalized electrons contribute to aromatic stabilization.
3. Connect structure and reactivity: The correct answer is Its ring has a delocalized system of pi electrons that gives unusual stability.

Correct answer: A

The correct answer is The hydroxyl group creates a polar bond and can hydrogen-bond with other molecules.

1. Identify the organic chemistry concept: Determine whether the question concerns carbon structure, hydrocarbons, nomenclature, functional groups, reactions, polymers, or laboratory analysis.
2. Apply the structural principle: The electronegative oxygen in the hydroxyl group creates polarity and hydrogen-bonding ability.
3. Connect structure and reactivity: The correct answer is The hydroxyl group creates a polar bond and can hydrogen-bond with other molecules.

Correct answer: B

The correct answer is An attraction involving hydrogen bonded to an electronegative atom and a lone pair on another electronegative atom.

1. Identify the organic chemistry concept: Determine whether the question concerns carbon structure, hydrocarbons, nomenclature, functional groups, reactions, polymers, or laboratory analysis.
2. Apply the structural principle: Hydrogen bonding is an intermolecular attraction that can strongly affect boiling point and solubility.
3. Connect structure and reactivity: The correct answer is An attraction involving hydrogen bonded to an electronegative atom and a lone pair on another electronegative atom.