Correct Answer: B

Rationale: The correct answer is B: Protons and neutrons only. Electrons are located outside the nucleus in electron shells. Protons and neutrons are the subatomic particles found within the nucleus of an atom. Protons carry a positive charge, while neutrons are neutral. These particles contribute to the mass and stability of the nucleus.
Choice A is incorrect because electrons are not part of the nucleus.
Choice C is incorrect as electrons are not found within the nucleus, only protons and neutrons.
Choice D is incorrect as protons and neutrons are indeed constituents of an atomic nucleus.

Correct Answer: D

Rationale: - Chromosomal nondisjunction is the failure of homologous chromosomes or sister chromatids to separate properly during cell division, leading to an abnormal number of chromosomes in the resulting cells.
- Down syndrome is caused by an extra copy of chromosome 21, resulting from nondisjunction during meiosis. Individuals with Down syndrome have three copies of chromosome 21 instead of the usual two.
- Turner syndrome is characterized by the absence of one X chromosome in females, leading to a variety of physical and developmental features.
- Klinefelter syndrome features one or more extra X chromosomes in males, typically resulting in infertility and other physical characteristics.


Therefore, chromosomal nondisjunction can lead to various genetic disorders such as Down syndrome, Turner syndrome, and Klinefelter syndrome, making option D the correct answer.

Correct Answer: B

Rationale: Ductility is the property of a substance that allows it to be drawn into thin wires without breaking. Conductivity refers to the ability of a substance to conduct electricity or heat, not to be drawn into wires. Viscosity is the measure of a fluid's resistance to flow, not related to the ability to be drawn into wires. Malleability is the property of a substance that allows it to be hammered or rolled into thin sheets, not specifically related to being drawn into wires.
Therefore, the correct property for the ability to be drawn into thin wires is ductility.

Correct Answer: B

Rationale: Benzene is indeed an example of an aromatic hydrocarbon. Aromatic hydrocarbons are characterized by having a cyclic structure with alternating single and double bonds (pi bonds). Benzene fits this description, making it aromatic. On the other hand, ethane, propane, and butene are aliphatic hydrocarbons, which do not have the distinct cyclic structure of aromatic hydrocarbons. Ethane, propane, and butene are aliphatic hydrocarbons, which contain only single bonds and are not cyclic in nature.
Therefore, they are not examples of aromatic hydrocarbons.

Correct Answer: C

Rationale: Power is the rate at which work is done or energy is transferred. The unit of measurement for power is the watt (W), named after James Watt, the inventor of the steam engine. The watt is defined as one joule per second, where a joule (J) is the unit of energy.
Choice A, Joule (J), is incorrect because a joule is a unit of energy, not power.
Choice B, Newton (N), is incorrect as a Newton is a unit of force, not power.
Choice D, Kilogram-meter (kg·m), is incorrect as it represents a unit of torque, not power.
Therefore, the correct answer is C: Watt (W).