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Which of the following substances protects the skin from ultraviolet radiation?

Melanin.

Perspiration.

Sebum.

Keratin.

Answer and Explanation

The Correct Answer is A

Melanin is a pigment produced by cells called melanocytes in the skin.

It protects the skin from ultraviolet (UV) radiation by absorbing and dissipating over 99.9% of absorbed UV radiation.

This helps to prevent DNA damage and other adverse effects of UV radiation on the skin.

Choice B. Perspiration is not correct because it is a fluid produced by sweat glands in the skin that helps to regulate body temperature, but it does not protect the skin from UV radiation.

Choice C. Sebum is not correct because it is an oily substance produced by sebaceous glands in the skin that helps to lubricate and protect the skin, but it does not protect the skin from UV radiation.

Choice D. Keratin is not correct because it is a fibrous protein that provides strength and durability to the skin, hair and nails, but it does not protect the skin from UV radiation.

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Correct Answer is C

Explanation

The pH scale is a logarithmic scale that measures the acidity or alkalinity of a solution.

A solution with a pH of 7 is neutral, while a solution with a pH less than 7 is acidic and a solution with a pH greater than 7 is alkaline.

Because the pH scale is logarithmic, each whole number change in pH represents a tenfold change in acidity or alkalinity.

Therefore, a substance with a pH of 3 is 10 times more acidic than a substance with a pH of 4.

Choice A. A substance with a pH of 3 is two times more alkaline than a substance with a pH of 4 is not correct because it incorrectly states that the substance with a lower pH is more alkaline and also incorrectly states the magnitude of the difference in acidity or alkalinity.

Choice B. A substance with a pH of 3 is two times more acidic than a substance with a pH of 4 is not correct because it correctly states that the substance with a lower pH is more acidic but incorrectly states the magnitude of the difference in acidity.

Choice D. A substance with a pH of 3 is 10 times more alkaline than a substance with a pH of 4 is not correct because it incorrectly states that the substance with a lower pH is more alkaline.

A. Titration. B. Electrophoresis. C. Filtration. D. Spectrophotometry.

Correct Answer is B

Explanation

Electrophoresis is a technique that uses an electric field to separate charged molecules, such as DNA fragments, based on their size and charge.

Choice A is not correct because titration is a laboratory method used to determine the concentration of a solution.

Choice C is not correct because filtration is a laboratory method used to separate solids from liquids.

Choice D is not correct because spectrophotometry is a laboratory method used to measure the absorbance of light by a solution.

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Solution in bag	Solution outside bag	Bag mass change (g):
water	Water	-0.2
20% sucrose	Water	+2.4
, 40% sucrose	Water	+4.3
, 60% sucrose	water	+5.8

Which of the following substances protects the skin from ultraviolet radiation?

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Naxlex Comprehensive Predictor Exams

Which of the following is correct regarding the pH scale?

Correct Answer is C

Explanation

To separate genomic DNA fragments by size, which of these laboratory methods is most useful?

Correct Answer is B

Explanation

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