1. Acne vulgaris, commonly known as acne, is primarily caused by

A. Dry skin (Dry skin can worsen acne but isn't the primary cause)
B. Clogged pores and excess oil production
C. Bacterial infection alone (Bacteria play a role but not the sole cause)
D. Vitamin deficiency

Correct answer: B

Rationale: The correct answer is B: 'Clogged pores and excess oil production.' Acne vulgaris, or acne, is primarily caused by a combination of factors including excess sebum (oil) production by the skin's sebaceous glands and the accumulation of dead skin cells, leading to clogged pores. This environment provides a breeding ground for acne-causing bacteria, contributing to inflammation and the formation of pimples. While factors like dry skin, bacterial infections, and even vitamin deficiencies can exacerbate acne, they are not the primary cause. Thus, B is the most accurate option for the primary cause of acne.

2. Which property of a substance describes its ability to conduct heat or electricity?

A. Reactivity
B. Conductivity
C. Density
D. Viscosity

Correct answer: b

Rationale: Conductivity refers to a substance's ability to conduct heat or electricity

3. A car skids on a wet road. What is the main force preventing the car from stopping?

A. Friction
B. Gravitational force
C. Normal force from the road
D. Air resistance

Correct answer: A

Rationale: Friction opposes the motion of the car, trying to bring it to a stop. However, due to the wet surface, the friction force is not enough to overcome the car's inertia.

4. What is the oxidation state of carbon in CH4?

A. +1
B. -1
C. +2
D. -4

Correct answer: d

Rationale: Each hydrogen atom has an oxidation state of +1, and the sum of oxidation states in CH4 is 0. Therefore, carbon has an oxidation state of -4.

5. Which hormone, produced by the pineal gland, plays a role in regulating sleep-wake cycles and is often associated with the body's internal circadian rhythm?

A. Melatonin
B. Serotonin
C. Dopamine
D. Endorphin

Correct answer: a

Rationale: The correct answer is A: Melatonin. Melatonin is a hormone produced by the pineal gland that plays a crucial role in regulating sleep-wake cycles and is closely tied to the body's circadian rhythm. It is often referred to as the 'sleep hormone' because it helps signal to the body when it is time to sleep and wake up. Serotonin (option B) is a neurotransmitter that plays a role in mood regulation and happiness. Dopamine (option C) is involved in reward-motivated behavior and movement. Endorphins (option D) are neuropeptides that act as natural painkillers and contribute to feelings of pleasure. Therefore, Melatonin is the hormone associated with the body's internal circadian rhythm and sleep-wake cycles.

6. 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: While color change can be an indicator of a chemical reaction, it's not always present, and some reactions occur without a visible color change.