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What type of bond forms between elements when they share electrons?
- A. Covalent bond
- B. Ionic bond
- C. Metallic bond
- D. Hydrogen bond
Correct Answer: A
Rationale: The correct answer is A: Covalent bond. In a covalent bond, atoms share electrons, leading to the creation of a strong attraction that holds them together. This type of bond is characterized by the sharing of electron pairs between atoms, resulting in the formation of molecules. Choice B, Ionic bond, involves the transfer of electrons from one atom to another, creating charged ions that attract each other. Choice C, Metallic bond, refers to the sharing of electrons among a sea of delocalized electrons in a metal structure. Choice D, Hydrogen bond, is a weak electrostatic attraction between a hydrogen atom and an electronegative atom like oxygen or nitrogen, not involving the sharing of electrons.
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Which of the following substances is a common base found in household products?
- A. Sodium chloride (NaCl)
- B. Ammonia (NH₃)
- C. Vinegar
- D. Lemon juice
Correct Answer: B
Rationale: The correct answer is B, Ammonia (NH₃). Ammonia is commonly found in household products and is used in cleaning agents due to its alkaline properties. Sodium chloride (NaCl) is a common salt and not a base. Vinegar is acetic acid, which is acidic in nature. Lemon juice contains citric acid, making it acidic as well. Therefore, ammonia is the only base among the choices provided.
Which condition involves an overactive immune system attacking healthy tissues, leading to inflammation and damage?
- A. Immunodeficiency
- B. Autoimmune disease
- C. Allergy
- D. Cancer
Correct Answer: B
Rationale: Autoimmune diseases occur when the immune system mistakenly targets and attacks healthy tissues in the body, leading to inflammation and damage. This is different from immunodeficiency, where the immune system is weakened and unable to effectively protect the body against infections. Allergies involve an exaggerated immune response to harmless substances, while cancer is characterized by uncontrolled cell growth. Therefore, the correct answer is autoimmune disease (Choice B) as it specifically describes the scenario of an overactive immune system attacking healthy tissues, distinguishing it from the other conditions listed.
Which of the following statements about fungi is FALSE?
- A. They can be unicellular or multicellular
- B. They are all parasitic and cause disease in humans
- C. They play a vital role in decomposition and nutrient cycling
- D. Some are used in food production, like mushrooms
Correct Answer: B
Rationale: A) This statement is true. Fungi can exist in both unicellular (yeast) and multicellular (molds and mushrooms) forms.
B) This statement is false. While some fungi can be parasitic and cause diseases in humans, not all fungi exhibit this behavior. Many fungi are beneficial and play essential roles in ecosystems.
C) This statement is true. Fungi are crucial for decomposition and nutrient cycling in ecosystems. They break down organic matter and recycle nutrients back into the environment.
D) This statement is true. Some fungi, like mushrooms, are used in food production and are consumed by humans.
What is the primary function of the coronary arteries in the cardiovascular system?
- A. Carry oxygenated blood to the heart muscle
- B. Carry deoxygenated blood from the heart muscle
- C. Pump blood to the lungs for oxygenation
- D. Regulate blood pressure in the systemic circulation
Correct Answer: A
Rationale: The primary function of the coronary arteries is to carry oxygenated blood to the heart muscle. Oxygenated blood is crucial for providing nutrients and oxygen to the heart muscle cells, enabling the heart to work efficiently. Without this oxygenated blood supply, the heart muscle may not receive the required nutrients and oxygen, potentially resulting in heart damage or dysfunction. Choices B, C, and D are incorrect as coronary arteries do not carry deoxygenated blood from the heart muscle, pump blood to the lungs for oxygenation, or regulate blood pressure in the systemic circulation. The coronary arteries specifically supply oxygenated blood to the heart muscle to support its function and vitality.
Which of the following is NOT a characteristic of a chemical reaction?
- A. Formation of new substances
- B. Release or absorption of energy
- C. Change in color
- D. Change in temperature
Correct Answer: C
Rationale: A change in color is not always a characteristic of a chemical reaction. While some chemical reactions may result in a change in color, it is not a universal characteristic of all chemical reactions. The formation of new substances, release or absorption of energy, and change in temperature are commonly associated with chemical reactions. Therefore, the correct answer is C, as it does not always occur in every chemical reaction.