1. The primary function of the respiratory system is to:

A. Maintain body temperature
B. Deliver oxygen to the bloodstream and remove carbon dioxide
C. Produce antibodies for the immune system
D. Break down food molecules for energy

Correct answer: B

Rationale: The correct answer is B: 'Deliver oxygen to the bloodstream and remove carbon dioxide.' The primary function of the respiratory system is to facilitate gas exchange. When we breathe in, oxygen is inhaled and transported to the bloodstream, where it is delivered to cells for energy production. Simultaneously, carbon dioxide, a waste product of cellular metabolism, is removed from the bloodstream and exhaled. This process is vital for sustaining life and maintaining proper oxygen levels in the body. The respiratory system does not primarily regulate body temperature, produce antibodies, or break down food molecules for energy, making options A, C, and D incorrect.

2. What is the pH of a solution with a hydrogen ion concentration of $1 \times 10^{-9}$ M?

A. 5
B. 7
C. 9
D. 11

Correct answer: c

Rationale: The pH is calculated as the negative logarithm (base 10) of the hydrogen ion concentration. In this case, $-\log(1 \times 10^{-9}) = 9$.

3. A honeycomb cell has six equal sides, each measuring 8mm. What is its perimeter?

A. 32mm
B. 40mm
C. 48mm
D. 56mm

Correct answer: C

Rationale: Multiply the side length by the number of sides: perimeter = number of sides * side length = 6 * 8mm = 48mm.

4. A ball is thrown horizontally off a cliff with a speed of 10 m/s. What is the horizontal distance the ball travels before hitting the ground?

A. 10 m
B. 20m
C. 30m
D. Cannot be determined without knowing the height of the cliff

Correct answer: C

Rationale: When a ball is thrown horizontally, its horizontal velocity remains constant throughout its motion. The time taken to hit the ground is determined by the vertical motion, which is independent of the horizontal velocity. Therefore, the horizontal distance traveled by the ball is determined by the horizontal velocity and the time taken to hit the ground. In this case, the horizontal distance is calculated as distance = velocity Ã— time = 10 m/s Ã— time. Since the horizontal velocity is 10 m/s and the time taken to hit the ground is determined by the vertical motion, the horizontal distance traveled by the ball is 10 m/s Ã— time. Without knowing the height of the cliff, we can still determine the horizontal distance traveled by the ball, which is 10 m/s Ã— time.

5. What happens when an atom loses an electron?

A. It becomes a molecule.
B. It gains a positive charge and becomes an ion.
C. It changes its element identity.
D. Nothing happens, it remains neutral.

Correct answer: B

Rationale: It gains a positive charge and becomes an ion. Losing an electron disrupts the charge balance, leaving the atom with more protons than electrons and a positive charge.

6. Laser light differs from typical light sources due to its properties of:

A. Enhanced brightness only
B. Monochromatic nature (single color) and coherence (synchronized waves)
C. Increased velocity
D. Limited visibility to the human eye

Correct answer: B

Rationale: The correct answer is B: Monochromatic nature (single color) and coherence (synchronized waves). Laser light is unique because it consists of a single color (monochromatic) and its waves are synchronized (coherent), unlike typical light sources which emit a range of colors and incoherent waves. This coherence allows laser light to stay focused over long distances, making it useful in various applications such as surgery, communication, and manufacturing. Enhanced brightness (A) is not the only distinguishing factor of laser light, as coherence and monochromatic nature are equally important. Increased velocity (C) and limited visibility to the human eye (D) are not properties that define laser light. Therefore, option B is the most accurate choice.