Correct Answer: A

Rationale: To convert liters to milliliters, you multiply the number of liters by 1000. Therefore, 0.5 liters equals 500 milliliters. This conversion is standard in various fields, making choice A the correct answer. Choices B, C, and D are incorrect because they do not correctly convert liters to milliliters.

Correct Answer: A

Rationale: To convert milligrams to micrograms, you need to multiply by 1000 because there are 1000 micrograms in a milligram. Therefore, 0.025 mg x 1000 = 25 mcg. This means that the correct answer is A, 25 mcg. Choice B, 250 mcg, is incorrect because it incorrectly multiplies by 10 instead of 1000. Choice C, 2.5 mcg, is incorrect as it inaccurately divides the value by 10. Choice D, 0.25 mcg, is also incorrect as it divides the value by 100 instead of multiplying by 1000.

Correct Answer: A

Rationale: The correct answer is A: 10^-9 meters. 1 nanometer (nm) is equivalent to 10^-9 meters. This conversion is commonly used in various scientific fields, including nanotechnology, to represent extremely small lengths. Choice B, 10^-6 meters, is incorrect as it represents a micrometer, not a nanometer. Choice C, 10^-12 meters, is incorrect as it would be a picometer, which is smaller than a nanometer. Choice D, 10^-15 meters, is incorrect as it would be a femtometer, much smaller than a nanometer.

Correct Answer: A

Rationale: The correct answer is A: 1 kilometer. 10^6 meters is equivalent to 1 kilometer, not 1 megameter. The prefix 'kilo-' represents a factor of 10^3 or one thousand, which is the appropriate conversion in this case. Choice B, 1 megameter, would be 10^6 meters squared. Choices C and D, 1 gigameter and 1 terameter, would represent even larger distances, as 'giga-' represents 10^9 and 'tera-' represents 10^12.

Correct Answer: B

Rationale: The correct answer is B: Liters. In the metric system, liters are the base unit for liquid volume. Milliliters, though a metric unit, are a smaller unit of volume and not the base unit. Gallons, on the other hand, are part of the imperial system and not a metric unit for volume. Option D is a duplicate of option B, making it incorrect.