Nokea
Which of the following substances is typically a good conductor of electricity when dissolved in water?
- A. Sugar
- B. Sodium chloride
- C. Olive oil
- D. Oxygen gas
Correct Answer: B
Rationale: Sodium chloride (table salt) is typically a good conductor of electricity when dissolved in water because it dissociates into ions (sodium cations and chloride anions) that can carry an electric current. Sugar (choice A), olive oil (choice C), and oxygen gas (choice D) do not dissociate into ions in water and therefore are not good conductors of electricity. Sugar does not dissociate into ions in water, so it cannot conduct electricity. Olive oil and oxygen gas are nonpolar substances and do not ionize in water, making them poor conductors of electricity.
You may also like to solve these questions
What is the main function of peroxisomes in the cell?
- A. To break down hydrogen peroxide
- B. To synthesize lipids and other cellular components
- C. To package and transport proteins
- D. To store genetic material
Correct Answer: A
Rationale: Peroxisomes are membrane-bound organelles found in eukaryotic cells that contain enzymes involved in various metabolic processes. One of the main functions of peroxisomes is to break down hydrogen peroxide, a toxic byproduct of metabolism, into water and oxygen through the action of the enzyme catalase. This process helps protect the cell from oxidative damage caused by hydrogen peroxide. While peroxisomes are involved in other metabolic functions such as lipid metabolism and the synthesis of bile acids, their primary role is the breakdown of hydrogen peroxide. Choices B, C, and D are incorrect because peroxisomes are not primarily responsible for synthesizing lipids, packaging and transporting proteins, or storing genetic material within the cell.
What is the mass number of an element?
- A. The number of protons in an atom's nucleus.
- B. The number of neutrons in an atom's nucleus.
- C. The number of electrons in an atom's valence shell.
- D. The number of isotopes of an element.
Correct Answer: B
Rationale: The mass number of an element represents the total number of protons and neutrons in an atom's nucleus. It specifically focuses on the number of neutrons in an atom's nucleus, which contributes to the overall mass of the atom. Therefore, the mass number is not solely determined by the number of protons, electrons, or isotopes. Choice A is incorrect because it refers to the atomic number, which is the number of protons in an atom's nucleus. Choice C is incorrect as the number of electrons in the valence shell is related to the atom's reactivity and bonding behavior, not the mass number. Choice D is incorrect because the mass number does not represent the number of isotopes of an element, but rather the sum of protons and neutrons in an atom's nucleus. Thus, option B, the number of neutrons in an atom's nucleus, is the correct choice.
Which of the following is the main organ responsible for storing energy?
- A. Liver
- B. Heart
- C. Kidneys
- D. Adipose tissue
Correct Answer: D
Rationale: Adipose tissue, commonly known as body fat, is the main organ responsible for storing energy in the form of triglycerides. It serves as a reserve of energy that can be utilized when needed. The liver primarily regulates glucose levels and stores glycogen for short-term energy needs but is not the main organ for long-term energy storage. The heart's main function is to pump blood throughout the body and is not involved in energy storage. The kidneys are essential for filtering blood and maintaining fluid balance but are not responsible for storing energy.
Two identical balls, one made of clay and the other made of steel, are dropped from the same height. Which ball reaches the ground first, neglecting air resistance?
- A. The clay ball due to its lower density
- B. The steel ball due to its higher density
- C. Both balls reach the ground simultaneously
- D. It depends on the initial velocities of the balls
Correct Answer: C
Rationale: In the absence of air resistance, both balls will experience the same acceleration due to gravity (9.8 m/s^2) regardless of their densities or materials. This means that both balls will reach the ground at the same time, assuming they are dropped from the same height simultaneously. The differences in density or material composition do not affect the rate at which objects fall in a vacuum. Therefore, both the clay and steel balls, being identical in shape and starting position, will have the same free-fall acceleration and will hit the ground simultaneously. Choices A and B are incorrect because the density of the materials does not impact the time it takes for objects to fall under gravity alone. Choice D is incorrect as the initial velocities do not play a role in the time taken to fall in a vacuum, where only the acceleration due to gravity affects the motion.
After exposure to a pathogen, the immune system develops memory. What type of immune cell is responsible for this immunological memory?
- A. B cells
- B. T cells (specifically memory T cells)
- C. Phagocytes
- D. Natural killer cells
Correct Answer: A
Rationale: B cells are responsible for immunological memory. Memory B cells, a type of B cells, retain a 'memory' of specific pathogens, enabling them to rapidly produce antibodies upon re-exposure. This rapid antibody production facilitates a quicker and more effective immune response. Although memory T cells also contribute to immunological memory by mounting a swift and robust immune response upon re-exposure to the pathogen, it is primarily memory B cells that play a crucial role in producing antibodies. Phagocytes are important immune cells involved in engulfing and digesting pathogens, while natural killer cells are primarily responsible for recognizing and eliminating abnormal cells, such as virus-infected cells or tumor cells. However, when it comes to immunological memory and antibody production, B cells are key players.