Chemistry
What is the atomic number of an element?
A. The number of neutrons, B. The number of protons, C. The number of electrons and neutrons combined, D. The mass number
Answer: B. The number of protons
Explanation: The atomic number is equal to the number of protons in the nucleus of an atom.
What is the formula for magnesium chloride?
(Mg has a charge of 2+, Cl has a charge of 1−)
A. MgCl, B. Mg₂Cl, C. MgCl₂, D. Mg₂Cl₂
Answer: C. MgCl₂
Explanation: Magnesium needs two chloride ions (each 1−) to balance its 2+ charge.
What is the basic unit of life?
A. Atom, B. Organ, C. Cell, D. Molecule
Answer: C. Cell
Explanation: All living organisms are made up of cells, which are the smallest units that can carry out life processes.
What is the correct formula for calculating average speed? A. Speed = time ÷ distance,
B. Speed = distance × time, C. Speed = distance ÷ time, D. Speed = distance + time
Answer: C. Speed = distance ÷ time
Explanation: Average (mean) speed is found by dividing the total distance traveled by the time taken.
Which of these is a correct statement about force fields?
A. Force fields only exist in space, B. Force fields only push objects away, C. Gravity and magnetism are types of force fields, D. All force fields are visible
Answer: C. Gravity and magnetism are types of force fields
Explanation: A force field is an area where a force can be felt, like magnetic, electric, or gravitational fields.
Which of the following is the correct electron configuration for an oxygen atom (atomic number = 8)?
A. 2,6, B. 2,8, C. 8,2, D. 6,2
Answer: A. 2,6
Explanation: Oxygen has 8 electrons: 2 fill the first shell, and 6 go in the second.
How many atoms are in one molecule of glucose (C₆H₁₂O₆)? A. 3, B. 6, C. 18, D. 24
Answer: c. 24
Explanation: Add all the atoms: 6 (C) + 12 (H) + 6 (O) = 24 atoms.
Which of the following structures is found in plant cells but not in animal cells?
A. Mitochondria, B. Cytoplasm, C. Cell wall, D. Nucleus
Answer: C. Cell wall
Explanation: The cell wall gives structure and support to plant cells and is not present in animal cells.
What is terminal velocity?
A. The speed a rocket must reach to escape gravity, B. The constant speed a falling object reaches when gravity and air resistance balance, C. The highest speed a car engine can produce, D. The minimum speed required for orbit
Answer: B. The constant speed a falling object reaches when gravity and air resistance balance
Explanation: Terminal velocity is when the downward force of gravity is balanced by the upward force of air resistance.
Which of the following shows acceleration on a speed–time graph? A. A flat horizontal line,
B. A line going down, C. A line going up, D. A curved line
Answer: C. A line going up
Explanation: A line sloping upward on a speed–time graph shows increasing speed—acceleration.
Explain how to write the electron configuration of an element. Use sodium (Na, atomic number = 11) as an example.
Answer:
Sodium has 11 electrons. The first shell can hold 2, the second can hold 8, and the third gets the remaining 1. So the configuration is 2,8,1.
Explanation: Electrons fill up energy levels (shells) in order: 2 in the first, up to 8 in the second, and so on.
Which of the following is an example of an exothermic reaction? A. Photosynthesis, B. Melting ice, C. Combustion of fuel, D. Cooking an egg
Answer: C. Combustion of fuel
Explanation: Exothermic reactions release energy in the form of heat or light—like burning fuel.
What does biodiversity refer to? A. The number of humans in an area, B. The number of different habitats in an area, C. The variety of living organisms in an area, D. The amount of pollution in an ecosystem
Answer: C. The variety of living organisms in an area
Explanation: Biodiversity includes the diversity of species, ecosystems, and genetic variations.
What is the moment of a force?
A. The speed at which force is applied, B. The force that causes acceleration, C. The turning effect of a force, D. The amount of energy stored
Answer: C. The turning effect of a force
Explanation: A moment is the force multiplied by the perpendicular distance from the pivot—it causes rotation.
Which of these is a correct statement about force fields? A. Force fields only exist in space, B. Force fields only push objects away, C. Gravity and magnetism are types of force fields, D. All force fields are visible
Answer: C. Gravity and magnetism are types of force fields
Explanation: A force field is an area where a force can be felt, like magnetic, electric, or gravitational fields.
Which of the following compounds contains a covalent bond? A. NaCl, B. H₂O, C. CaCl₂, D. MgO
Answer: B. H₂O
Explanation: Water is made of non-metal atoms (hydrogen and oxygen) that share electrons, forming covalent bonds.
What is the main difference between exothermic and endothermic reactions?
Answer:
Exothermic reactions release heat, while endothermic reactions absorb heat.
Explanation: In exothermic reactions, the temperature increases; in endothermic reactions, the surroundings get colder.
Which two main groups are used to classify all living things first? A. Plant and animal, B. Vertebrate and invertebrate, C. Bacteria and fungi, D. Kingdom and species
Answer: a. Plant and animal
Explanation: Traditionally, living organisms were first grouped into plant and animal kingdoms, though modern systems include more categories like fungi, protists, and bacteria.
Use the formula for work done to calculate the energy used when a 20 N force moves a box 3 m.
Answer:
Work = force × distance = 20 N × 3 m = 60 J
Explanation: Work is measured in joules (J), showing how much energy was transferred by the force.
A wrench is used to tighten a bolt. If a force of 50 N is applied at a distance of 0.3 m from the bolt, calculate the moment. Why is it easier to turn the bolt with a longer wrench?
Answer:
Moment = Force × Distance = 50 N × 0.3 m = 15 Nm.
It is easier to turn the bolt with a longer wrench because the distance from the pivot is greater. This increases the moment, making it easier to rotate the bolt.
Explanation:
Increasing the distance increases the turning effect for the same force, following the formula for moment.
Balance this equation:
__H₂ + __O₂ → __H₂O
Answer:
2H₂ + O₂ → 2H₂O
Explanation: There are 4 hydrogen atoms and 2 oxygen atoms on both sides of the equation.
Is the reaction of vinegar and baking soda endothermic or exothermic? How do you know?
Answer:
Endothermic – the mixture becomes cooler during the reaction.
Explanation: Energy is absorbed during the formation of new products (carbon dioxide, water, etc.).
Which of the following is not a characteristic of living things? A. They grow and develop, B. They respond to stimuli, C. They can reproduce
D. They always move from place to place
Answer: D. They always move from place to place
Explanation: Not all living things move from place to place (e.g., plants), but they all respond to their environment.
Calculate the weight of a 2 kg object on Earth (g = 10 N/kg).
Answer:
Weight = mass × gravitational field strength = 2 kg × 10 N/kg = 20 N
Explanation: Weight is the force of gravity on a mass, measured in Newtons (N).
How can you increase the turning effect of a force? Give two ways and explain why.
Answer:
You can increase the turning effect by:
Applying a larger force.
Increasing the distance from the pivot where the force is applied.
Both methods increase the moment because moment = force × distance.
Explanation:
By increasing either variable in the moment formula, the overall moment increases, making it easier to cause rotation.