Nursing Elites

1. How does sunscreen protect the skin from harmful ultraviolet (UV) rays?

• A. By reflecting UV rays away from the skin
• B. By absorbing UV rays and converting them to heat
• C. By blocking UV rays completely
• D. By stimulating melanin production

Correct answer: B

Rationale: Sunscreen works by absorbing UV rays and converting them to heat. This mechanism helps to prevent the UV rays from penetrating the skin and causing damage such as sunburn, premature aging, and skin cancer. Reflecting UV rays away from the skin (option A) is not the primary function of sunscreen. While sunscreen does block UV rays, it does not do so completely (option C) as some UV rays may still penetrate the skin. Sunscreen does not stimulate melanin production (option D) as a means of protecting the skin from UV rays.

2. Which of the following properties is NOT characteristic of a covalent bond?

• A. Sharing of electrons between atoms
• B. High melting and boiling points
• C. Low electrical conductivity in solid state
• D. Directional bonding

Correct answer: B

Rationale: Covalent bonds are formed by the sharing of electrons between atoms, leading to the formation of molecules with directional bonding. This means that the atoms are held together in a specific orientation. Covalent compounds generally exhibit low melting and boiling points compared to ionic compounds due to the weaker intermolecular forces present in covalent compounds. Furthermore, covalent compounds do not conduct electricity in the solid state because the electrons are localized between the atoms and are not free to move and carry charge. Hence, high melting and boiling points are not characteristic of covalent bonds. The correct answer is 'B' because high melting and boiling points are typically associated with ionic compounds due to their strong electrostatic interactions, while covalent compounds have lower melting and boiling points. Choices A, C, and D are all characteristics of covalent bonds, making them incorrect answers for this question.

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

• A. +1
• B. -1
• C. +2
• D. -4

Correct answer: D

Rationale: In CH4 (methane), carbon is bonded to four hydrogen atoms. Hydrogen has an oxidation state of +1. Since the overall charge of CH4 is 0, the oxidation state of carbon must be -4 to balance the charges. Each hydrogen contributes an oxidation state of +1, resulting in a total of +4 from hydrogen atoms. To achieve a total oxidation state of 0 for the molecule, carbon must have an oxidation state of -4 to offset the contribution from hydrogen. Therefore, the correct answer is -4. Choices A, B, and C are incorrect: +1 is the oxidation state of hydrogen, -1 is not the oxidation state of carbon in methane, and +2 is not the correct oxidation state of carbon in CH4.

4. A car brakes to a stop on a level road. Which of the following forces does NOT do work on the car?

• A. The braking force applied by the wheels
• B. The normal force from the road
• C. The gravitational force on the car
• D. The friction force between the tires and the road

Correct answer: B

Rationale: The normal force from the road does not do work on the car because it is perpendicular to the direction of motion. Work is defined as force applied in the direction of motion, so the normal force, which acts perpendicular to the motion of the car, does not contribute to the work done on the car. The braking force applied by the wheels, the gravitational force on the car, and the friction force between the tires and the road all act in the direction of motion and contribute to the work done on the car. In this scenario, the normal force is supporting the weight of the car and keeping it from sinking into the road, but it does not transfer energy to the car as it moves.

5. Which property of a substance refers to its ability to be stretched into thin wires without breaking?

• A. Conductivity
• B. Viscosity
• C. Ductility
• D. Malleability

Correct answer: C

Rationale: Ductility is the property of a substance that allows it to be stretched into thin wires without breaking. This property is distinct from the other options provided. Conductivity refers to the ability to conduct electricity or heat, viscosity refers to a liquid's resistance to flow, and malleability refers to the ability of a substance to be hammered or rolled into thin sheets. Therefore, the correct answer is 'Ductility.'

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