Pond silk or water silk is the common name of a. Nostac b. spirogyra
c. chalamydomonas d. peziza

B

Explanation:

Spirogyra is free-floating green algae present in freshwater habitats such as ponds, lakes, etc. Spirogyra is commonly known as water silk or pond silk. They have a filamentous and unbranched vegetative structure.

or

Spirogyra forms a silk like layer on the water. It is present in abundant amount on the fresh water bodies or slow running water. They are slippery in nature, so are commonly known as pond silk or water silk.