Nokea
What is the difference between a pure substance and a mixture?
- A. Pure substances have a fixed composition, mixtures don't.
- B. Mixtures have a fixed composition, pure substances don't.
- C. Pure substances can be in any state, mixtures are not always solids.
- D. Pure substances are always elements, mixtures are always compounds.
Correct Answer: A
Rationale: Pure substances have a definite and constant composition, meaning they are made up of only one type of atom or molecule with fixed proportions. This composition does not vary. On the other hand, mixtures are composed of two or more substances physically combined. The components of a mixture can be present in varying proportions, leading to a variable composition. Choice A is correct as it accurately distinguishes between pure substances and mixtures based on the fixed composition of pure substances and the variable composition of mixtures. Choice B is incorrect because mixtures, not pure substances, have variable compositions. Choice C is incorrect as both pure substances and mixtures can exist in different states. Choice D is incorrect because pure substances can be compounds as well, not exclusively elements, and mixtures can contain elements and compounds.
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Which of the following can weaken the immune system and increase susceptibility to infections?
- A. Regular exercise
- B. Balanced diet
- C. Chronic stress
- D. Adequate sleep
Correct Answer: C
Rationale: Chronic stress can weaken the immune system by increasing the production of stress hormones like cortisol, which can suppress the immune response. This suppression can make individuals more susceptible to infections and illnesses. Conversely, regular exercise, a balanced diet, and adequate sleep actually support a healthy immune system and help strengthen it. Choices A, B, and D are incorrect as they are factors that generally contribute positively to the immune system. Regular exercise, a balanced diet, and adequate sleep are crucial for maintaining overall health and boosting the immune system rather than weakening it.
Which property of matter refers to the measure of the force of gravity acting on an object?
- A. Mass
- B. Weight
- C. Density
- D. Volume
Correct Answer: B
Rationale: The correct answer is 'Weight.' Weight is the measure of the force of gravity acting on an object. Mass refers to the amount of matter in an object, density is the mass per unit volume of a substance, and volume is the amount of space an object occupies. In this context, the question specifically asks for the property related to the force of gravity, making 'Weight' the correct choice. 'Mass' is the measure of the amount of matter in an object, 'Density' is the mass per unit volume of a substance, and 'Volume' is the space occupied by an object, none of which directly measure the force of gravity on an object.
The number of protons in an atom determines its:
- A. Mass number
- B. Atomic number
- C. Atomic weight
- D. Valence electron count
Correct Answer: B
Rationale: The number of protons in an atom is known as the atomic number. The atomic number uniquely identifies an element and determines its position on the periodic table. It is a fundamental property of an element and directly influences its chemical behavior and interactions. The mass number, on the other hand, is the sum of protons and neutrons in the nucleus of an atom, not just protons. Atomic weight is the average mass of an element's isotopes considering their relative abundance, not solely based on the number of protons. Valence electron count refers to the number of electrons in the outermost energy level of an atom, influencing its ability to form bonds and participate in chemical reactions, but it is not determined by the number of protons in the atom.
Which neurotransmitter is associated with pleasure, reward, and motivation, and is often implicated in conditions such as addiction?
- A. Acetylcholine
- B. Dopamine
- C. Serotonin
- D. GABA (Gamma-aminobutyric acid)
Correct Answer: B
Rationale: Dopamine is the neurotransmitter associated with pleasure, reward, and motivation. It plays a crucial role in the brain's reward system and is often implicated in conditions such as addiction. Acetylcholine is involved in muscle movement and memory, serotonin is linked to mood regulation, and GABA is an inhibitory neurotransmitter that helps reduce neuronal excitability. Therefore, the correct answer is dopamine as it aligns with the neurotransmitter functions related to pleasure, reward, and motivation, distinct from the roles of acetylcholine, serotonin, and GABA.
Which sexually transmitted infection (STI) can potentially cause infertility in both men and women if left untreated?
- A. Human papillomavirus (HPV)
- B. Chlamydia
- C. Gonorrhea
- D. Syphilis
Correct Answer: B
Rationale: Chlamydia is the correct answer because if left untreated, it can lead to serious complications such as pelvic inflammatory disease (PID) in women and epididymitis in men, both of which can cause infertility. Chlamydia is a common sexually transmitted infection that often presents with no symptoms, making it important for individuals to get tested regularly, especially if they are sexually active. It is crucial to detect and treat Chlamydia early to prevent long-term consequences such as infertility. Human papillomavirus (HPV) can lead to genital warts and certain types of cancer but is not typically associated with infertility. Gonorrhea and syphilis can cause serious health problems if untreated, but infertility is more commonly associated with Chlamydia.