Photochemistry Multiple Choice Questions and Answers

1 The fact that the fluorescence wavelength is often much longer than the irradiation wavelength (Stokes shift) is a consequence of which phenomenon?

A the Franck–Condon principle

B low extinction coefficients (Lambert-Beer law)

C vertical transitions (Kasha’s rule)

D high ISC rates (El Sayed rule)

View Answer

Answer: the Franck–Condon principle

2 The quantum efficiency of a photochemical reaction is defined as _______

A ratio of molecules decomposed in a given time to the number of quanta absorbed in the same time

B number of 11101ecules decomposed in a given time

C number or quanta absorbed percent time

D ratio of’ molecules decomposed in a given time to the number of quanta emitted in the same time

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Answer: ratio of molecules decomposed in a given time to the number of quanta absorbed in the same time

3 Which of the following are the reactions in which molecules absorbing light do not themselves react but induce other molecules to react?

A Photosensitized reactions

B Free radical reactions

C Chain reactions

D Reversible reactions

View Answer

Answer: Photosensitized reactions

4 The reactions which are caused by heat and in absence of light is called _____

A Photochemical reactions

B Dark reactions

C Reversible reaction

D Reversible photochemical reaction

View Answer

Answer: Dark reactions

5 Ozone is formed by ______ dissociation of molecular oxygen into individual oxygen atoms.

A photochemical

B thermochemical

C thermal

D ionic

View Answer

Answer: photochemical

6 Which of the following is an example of photochemical reaction?

A Photosynthesis

B Decomposition of ammonia

C Formation of NaOH

D Decomposition of HCl

View Answer

Answer: Photosynthesis

7 Which of the following are the principle laws of photochemistry?

A Grothus-Draper and Stark-Einstein law

B Raoult’s and Dalton’s law

C Raoult’s and Henry’s law

D Lambert’s and Beer’s law

View Answer

Answer: Grothus-Draper and Stark-Einstein law

8 Mercaptans can be produced by photochemical addition of ______ to alpha olefins.

A Hydrogen Sulphide

B Sulphur

C Hydrogen

D Paraffins

View Answer

Answer: Hydrogen Sulphide

9 Vision is initiated by a photochemical reaction of ______

A Rhodopsin

B Enzymes

C Mercapton

D Hydrogen Chloride

View Answer

Answer: Rhodopsin

10 Medicine bottles are often made with darkened glass _______

A to prevent the drug from photodegradation

B to allow the photodegradation of drug

C to reduce the cost

D to allow oxidation of drug

View Answer

Answer: to prevent the drug from photodegradation

11 In _____ reactions, molecules absorbing light do not themselves react but induce other molecules to react.

A Photosensitized

B Dark

C Thermal

D Irreversible

View Answer

Answer: Photosensitized

12 In photochemical reactions, absorption of _____ radiations takes place.

A ultraviolet and visible

B radio

C only visible

D visible and x-rays

View Answer

Answer: ultraviolet and visible

13 A substance absorbs 2.0 x 1016 quanta or radiations per second and 0.002 mole of it reacts in 1200 seconds. What is the quantum yield or the reaction (N = 6.02 x 1023)?

A 50

B 100

C 40

D 80

View Answer

Answer: 50

14 Which of the following will result in deviation from Beer’s law? (A) Change in a refractive index of medium (B) Dissociation of analyte on dilution (C) Polychromatic light (D) Path length of cuvette

A A, B and C

B B, C and D

C A, C and D

D A, B and D

View Answer

Answer: A, B and C

15 A 0.1 M solution of compound A shows 50% transmittance when a cell of 1 cm width is used at λ1 nm. Another 0.1 M solution of compound B gives the optical density value of 0.1761 using 1cm cell at λ1 nm. What will be the transmittance of a solution that is simultaneously 0.1 M in A and 0.1 M in B using the same cell and at the same wave length? [log 1.301; log 1.4771; log 50 = 1.699].

A 33.3%

B 50%

C 66.7%

D 70%

View Answer

Answer: 33.3%

16 What are the appropriate reasons for the deviation from the Beer’s law among the following? (A) Monochromaticity of light (B) Very high concentration of analyte (C) Association of analyte (D) Dissociation of analyte

A A, B and D

B B, C and D

C A, C and D

D A, B and C

View Answer

Answer: B, C and D

17 The molar extinction coefficient of B (MW = 180) is 4 x 103 L mol-1 cm-1. One-liter solution of C which contains 0.1358 g pharmaceutical preparation of B, shows an absorbance of 0.411 in a 1 cm quartz cell. What is the percentage (w/w) of B in the pharmaceutical preparation?

A 13.60

B 29.12

C 10.20

D 20.40

View Answer

Answer: 13.60

18 Which of the following instruments is used to measure the energy of the monochromatic radiation most accurately?

A Thermopile

B The chemical actinometer

C Photoelectric cell

D The potential detector

View Answer

Answer: Thermopile

19 Which regions of the light radiations of the visible ultraviolet lying between – wavelength are chiefly concerned in bringing about photochemical reactions?

A 8000 Å and 2000 Å

B 19000 Å and 12,000 Å

C 1000 Å and 2000 Å

D 1500 Å and 1000 Å

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