Correct Answer: C

Rationale: The magnitude of the frictional force acting on the book sliding across a table is determined by both the mass of the book and the normal force from the table. Frictional force is proportional to the normal force (which is influenced by the weight of the book, i.e., its mass) and is affected by the surfaces in contact and other friction-related factors. Therefore, both the mass of the book and the normal force from the table are essential in determining the frictional force experienced by the book during its sliding motion. Choices A, B, and D are incorrect because friction is a result of the interaction between the surfaces and is influenced by both the mass of the object and the normal force acting on it.

Correct Answer: A

Rationale: Eczema is a skin condition characterized by red, itchy, and inflamed patches. It is a common condition that can vary in severity and often presents with symptoms such as dry, scaly skin, and sometimes oozing or crusting. Psoriasis, on the other hand, presents with red, scaly patches but is not typically described as itchy. Melanoma is a type of skin cancer characterized by the development of abnormal moles, while keloid is a type of raised scar that can occur after an injury to the skin. Therefore, the correct answer is eczema due to its specific symptom presentation of red, itchy, and inflamed patches.

Correct Answer: B

Rationale: The pH scale measures the acidity or basicity of a solution. A pH of 7 is considered neutral, indicating that the concentration of hydrogen ions (H+) is equal to the concentration of hydroxide ions (OH-) in the solution. A pH ranging from 0 to 6.9 signifies acidity, while a pH from 7.1 to 14 signifies alkalinity. Therefore, a neutral solution has a pH value of 7. Choice A (0) represents a highly acidic solution, Choices C (14) and D (-7) are outside the valid pH range and do not correspond to a neutral solution.

Correct Answer: B

Rationale: The correct answer is B: Iron. Hemoglobin, the protein responsible for carrying oxygen in red blood cells, contains iron in its heme group, contributing to the blood's characteristic red color. Magnesium (choice A), copper (choice C), and zinc (choice D) are not responsible for the red color of blood. Magnesium is an essential mineral involved in various physiological processes, copper is a trace element important for enzyme function, and zinc is a micronutrient essential for multiple cellular functions but not related to the red color of blood.

Correct Answer: B

Rationale: Elements within the same group share similar electron configurations in their outermost shell. The periodic table is organized based on the number of electrons in the outermost energy level, known as valence electrons, which significantly influence an element's chemical properties. Elements within the same group have the same number of valence electrons, leading to comparable chemical behaviors. Choices A and D are incorrect because elements within the same period, not group, have identical electron configurations, and an element's group is primarily determined by the number of valence electrons and not the number of electron shells. Choice C is incorrect because while electron configuration is crucial for understanding an element's properties, it is not the sole factor determining its position on the periodic table.