Question

Which of the following is a photosensitive element?

(a) S

(b) Se

(c) O

(d) Po

The question was posed to me in unit test.

My question is from P-Block in portion P-Block Elements of Chemistry – Class 12

Answer 1

Correct option is (b) Se

To elaborate: The grey form of Selenium (metallic) and Tellurium consist of parallel chains held by weak metallic bonds. In the presence of light, the weak metallic bonds are excited and as a result, the number of free electrons increases and so does the conductivity. Thus, these elements conduct electricity significantly only in the presence of light. That is why Se and Te are called photosensitive elements.