The goal of a sunscreen chemical is simpleto prevent harmful UVB (and

Question

The goal of a sunscreen chemical is simple—to prevent harmful UVB (and in some cases UVA) radiation from penetrating the skin. There are two main ways in which this goal can be accomplished—by reflecting (physically blocking) ultraviolet light or by absorbing UV light. Sunscreen chemicals are therefore put into two groups based on which method they employ; they are classified as either physical blockers or chemical absorbers. Physical blockers, the most common of which is titanium dioxide, scatter all radiation in the UVB and UVA range. Titanium dioxide reflects light waves in the 290–770 nm range. However, the vast majority of commercial sunscreens are chemical absorbers.

Chemical absorbing sunscreens work on the principle of photo-excitation of electrons. They absorb photons of light of specific wavelengths and use the energy to promote electrons between energy levels. When the electrons later return to the ground energy state, they emit light at longer wavelengths (lower energies). Chemical species that exhibit this behavior are called chromophores. The specific wavelength absorbed by a given chromophore is determined by the discrete quantal amounts of energy that are required to excite electrons between the energy levels or its molecules. Since the primary objective of an absorbing sunscreen is to absorb UVB light (290–320 nm), the best sunscreens are those that absorb most heavily in this range. The chromophores that most readily fit this requirement are those with conjugated pi-bonding systems.    1 
 1. Which of the following best summarizes the distinction between chemical blockers and chemical absorbers?

(A) Chemical blockers darken their target light waves while chemical absorbers lighten them.
(B) Chemical blockers convert their target light waves into radiation while chemical absorbers convert them into a different kind of radiation.
(C) Chemical blockers disperse their target light waves while chemical absorbers convert them into light with a longer wavelength.
(D) Chemical blockers scatter their target light waves while chemical absorbers convert them into radiation.
(E) Chemical blockers prevent light waves from reaching the skin while chemical absorbers absorb them into the skin.

2 
 2. Based on the passage, which of the following can be inferred about the chromophores referred to in the final sentence of the passage?

(A) If exposed to light with wavelengths of approximately 300 nm, they will scatter the radiation.
(B) If exposed to light with wavelengths in the 290–320 nm range, they will lower the energy level of some of their constituent electrons.
(C) If exposed to light waves in the 290–770 nm range, they will absorb the photons and emit them as light of longer wavelengths.
(D) If exposed to light with wavelengths of approximately 300 nm, some electrons in their component molecules will switch to higher energy levels.
(E) If exposed to light waves in the 290–320 nm range, they will promote the discrete quantal amounts of energy that are required to excite electrons between energy levels.

RC Butler 2023  -  Practice Two RC Passages Everyday.   
Passage # 154 Date: 18-May-2023
 This question is part of RC Butler 2023 .  Click here for Details

Manhattan GRE 5Ib.

Bonojit · Answer

Hi,

Could you please provide an explanation for the second question? I felt the correct option should be E as opposed to D. I couldn't infer the statement "some electrons in their component molecules will switch to higher energy levels" from the passage. Hence, I eliminated this option and went for E

Sajjad1994 · Answer

Official Explanation

2. Based on the passage, which of the following can be inferred about the chromophores referred to in the final sentence of the passage?

Explanation

The chromophores absorb light in the 290–320 nm range and use it to promote (or move up) electrons between energy levels. Since light with wavelengths of 300 nm falls in this range, their electrons should move up in energy levels when exposed to it.

(C)  would be correct if not for the range given: you don’t know how chromophores react to light above 320 nm.

(B)  is the exact opposite of what you are looking for.

(A)  applies to physical blockers but not to chemical absorbers.

Answer: D

mitul19 · Answer

Could you please provide the explanation for Q1 ?

Sajjad1994 · Answer

Official Explanation

1. Which of the following best summarizes the distinction between chemical blockers and chemical absorbers?

Difficulty Level:   600

Explanation

Chemical blockers scatter, or disperse, light waves. Chemical absorbers use light waves to promote electrons which then release light waves with a longer wavelength as they return to their ground energy state. Thus,  choice (C)  is correct.

Choice (A)  makes a reference to lightening and darkening light waves, neither of which is mentioned in the passage.

Choices (B)  and  (D)  refer to converting light waves to radiation, which is not mentioned in the passage. And absorbers absorb the radiation into their molecularstructure, not into the skin as in  choice (E).

Answer: C

Its_me_aka_ak · Answer

Why not E?
Yes, Chromos excite the electrons but they need discrete quantal amounts of energy to do so. Bingo

comparing to option D which says that 'some' components of molecules 'will switch' to higher levels.
there are 2 problems with this option as per my understanding.
1. nowhere in the passage there's mentioned that only 'some' get excited
2. they do not 'switch' to higher level  themselves  it is a process that includes photons

Sajjad1994 · Answer

Option (E)  suggests that the chromophores, when exposed to light waves in the 290–320 nm range, will promote the discrete quantal amounts of energy required to excite electrons between energy levels. This statement is incorrect based on the principles described in the passage. The correct behavior of chromophores in this context is that they absorb photons of specific wavelengths, promoting electrons to higher energy levels, not exciting electrons between energy levels in discrete quantal amounts.

In summary, the passage explains that the chromophores in chemical absorbing sunscreens absorb specific wavelengths of light (e.g., in the UVB range, 290–320 nm), promoting electrons to higher energy levels. When these electrons later return to the ground state, they emit light at longer wavelengths.

Option (E)  inaccurately describes the behavior of chromophores, making it an incorrect inference.

The goal of a sunscreen chemical is simpleto prevent harmful UVB (and

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The goal of a sunscreen chemical is simpleto prevent harmful UVB (and

Prep Toolkit

615 to 715 in 15 Days (Ria's Strategies)

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