Correct Answer: B

Rationale: The Pauli exclusion principle states that no two electrons in an atom can have the same set of four quantum numbers. This principle leads to the rule that electrons must have opposite spins when occupying the same orbital. Therefore, electrons cannot occupy the same orbital with the same spin, as stated in option B. Option A is incorrect as it refers to the Aufbau principle, which describes the order in which electrons fill orbitals based on increasing energy. Option C is incorrect as it provides the formula for the maximum number of electrons in an orbital based on the energy level, not the Pauli exclusion principle. Option D is incorrect as it describes Coulomb's law, which deals with the electrostatic force between charged particles, not the Pauli exclusion principle.

Correct Answer: A

Rationale: A) Tundra: This biome is characterized by cold temperatures, permafrost (permanently frozen subsoil), and vegetation such as mosses, lichens, and coniferous trees like spruce and fir. The tundra is found in high latitudes near the Arctic Circle and high altitudes in mountainous regions. It is a cold and harsh environment where the ground remains frozen for a significant part of the year. The coniferous trees in this biome are adapted to survive in extreme cold conditions. B) Desert: Deserts are characterized by low precipitation levels and high temperatures, with sparse vegetation adapted to arid conditions. C) Rainforest: Rainforests are characterized by high levels of rainfall, warm temperatures, and dense vegetation with a variety of plant and animal species. D) Savanna: Savannas are tropical grasslands with scattered trees and shrubs, characterized by a distinct wet and dry season. They have a different climate pattern compared to the cold temperatures and permafrost found in the tundra biome. In this case, the description of cold temperatures, permafrost, and coniferous trees aligns most closely with the characteristics of the tundra biome, making option A the correct answer.

Correct Answer: C

Rationale: The term 'reaction mixture' is used to describe the combination of both reactants and products that exist simultaneously during a chemical reaction. It encompasses not only the initial substances (reactants) but also the resulting compounds (products) formed throughout the reaction process. Choice A, 'Solution,' typically refers to a homogenous mixture where one substance is dissolved in another. Choice B, 'Mixture,' is a general term that does not specifically indicate the mix of reactants and products in a chemical reaction. Choice D, 'Precipitate,' specifically refers to the solid formed when two solutions react and a solid compound is produced.

Correct Answer: A

Rationale: The correct answer is A: Primary immune response. The primary immune response refers to the initial encounter with a specific pathogen, which triggers the development of the first immune response by the immune system. This response involves activating immune cells like B cells and T cells to produce antibodies and memory cells specific to that pathogen. On the other hand, the secondary immune response occurs upon re-exposure to the same pathogen and is characterized by a faster, stronger, and more effective immune response due to the presence of memory cells from the primary response. Choices B, C, and D are incorrect. The secondary immune response is the response upon re-exposure, hypersensitivity reactions are exaggerated immune responses to antigens, and immunological tolerance is the immune system's ability to recognize and tolerate self-antigens without mounting an immune response.

Correct Answer: C

Rationale: A) Unprotected sexual contact is a common route of transmission for sexually transmitted infections (STIs) as many STIs are spread through genital, anal, or oral sex without the use of barrier protection such as condoms. B) Sharing contaminated needles can also transmit STIs such as HIV and hepatitis B and C, especially among individuals who inject drugs. C) Deep kissing, while it can transmit certain infections like herpes simplex virus (HSV-1) or cytomegalovirus (CMV), is not a common route of transmission for most STIs. Although some STIs can be transmitted through saliva, deep kissing is not a primary mode of transmission for most STIs. D) Mother to child transmission during childbirth can occur with certain STIs such as HIV, syphilis, and herpes, where the infection can be passed from the mother to the baby during delivery. Therefore, deep kissing (option C) is the correct answer as it is not a typical route of transmission for most STIs.