Correct Answer: C

Rationale: To convert grams to milligrams, you multiply by 1000. So, 2751.4 g * 1000 = 2751.4 mg. Therefore, choice C (275.14 mg) is correct. Choice A is incorrect as it incorrectly moves the decimal point. Choice B is incorrect as it doesn't account for the conversion factor. Choice D is incorrect as it incorrectly uses scientific notation.

Correct Answer: C

Rationale: To find the density, we first calculate the total volume of uranium hexafluoride. Since each drum contains 15 L, the total volume is 30 drums * 15 L/drum = 450 L. Next, convert the mass from kg to g (1 kg = 1000 g). Density = mass/volume. Density = (mass in g) / (volume in mL). Since the mass is in g, we need to convert the volume from L to mL (1 L = 1000 mL). Density = (mass in g) / (volume in mL) = (mass in g) / (volume in L * 1000). Density = (mass in g) / (450 L * 1000) = (mass in g) / 450000 mL. Therefore, the density is the mass divided by 450000. The correct answer is C: 2.25 g/mL. Choice A is incorrect as it is too low

Correct Answer: A

Rationale: The correct answer is A: solid. Uranium hexafluoride has a melting point of 148°F, which is equivalent to approximately 64.4°C. Since the water temperature in the English Channel is only about 17°C, the uranium hexafluoride would be below its melting point and thus in a solid state. The other choices are incorrect because the temperature is not high enough for it to be in a liquid or gaseous state, and there is no indication of it being a mixture of solid and liquid based on the given information.

Correct Answer: D

Rationale: The correct answer is D: 4. Significant figures are non-zero digits and zeros between them. In this case, only digits 6, 4, 2, and 8 are non-zero, making them all significant. Zeros before the first non-zero digit are not significant, so the zeros before 6 are not counted. Hence, there are 4 significant figures in the number 0006428. Choice A (7) is incorrect because it includes all digits, including the leading zeros, which are not significant. Choice B (3) is incorrect because it only considers the non-zero digits, excluding the zeros between them. Choice C (8) is incorrect because it counts all digits including leading zeros, which are not significant.

Correct Answer: A

Rationale: The correct answer is A because gasoline has a lower density compared to water. Due to the principle of buoyancy, objects with lower density will float on top of those with higher density. Gasoline will float on top of water because it is less dense. Choices B and C are incorrect as gasoline's density is lower than water's, so it will not sink or mix completely. Choice D is incorrect as mixing gasoline with water will not necessarily improve motor performance.