Assertion: A butter paper acts as translucent medium for light
Reason: Translucent substances allow only a part of light through them
A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
B. Both Assertion and Reason are correct but Reason is not correct explanation for Assertion
C. Assertion is correct but Reason is incorrect
D. Both Assertion and Reason are incorrect

Hint: We need to know about translucent substances and how butter paper is related to it. Butter paper is a thin, non greasy paper which is used for various purposes. There are few substances which allow complete light to pass through i.e. transparent and some other substances which allow partial light to pass and i.e. translucent and the other substances which don't allow light to pass through i.e. opaque.

Complete answer:
Different substances based on their allowance of light are clear now. Let us now discuss butter paper and the properties related to it in relation to light. It is basically a translucent substance which allows partial light to pass through and is usually thin to allow gases diffusion. It is also resistant to heat and water. By the above discussion, both assertion and reason are right. The reason why it acts as a translucent medium is just because it allows some amount of light to pass through and that gives a correct explanation.

The correct answer is option A.

Note:
The butter paper is actually used during emasculation where you remove the male reproductive parts and close it with butter paper to prevent contamination from other pollen. This process where you cover the emasculated flower with a paper is termed as bagging. This technique is widely followed by breeders during artificial hybridization.