The standard size of herbarium sheet is
A. 11.5 inch x 16.5 inch
B. 15.5 inch x 16.5 inch
C. 18.5 inch x 10.5 inch
D. 20.5 inch x 21.5 inch

Hint: Plant specimens are preserved in dry state by the taxonomists. They mount the specimens onto a thick sheet of paper. Then, this mounted sheet of paper is called the herbarium sheet. These herbarium sheets are sequentially stored in place commonly known as the herbarium.

Complete answer:
Herbarium sheet is a most common method of permanent preservation of the plant specimens. This helps in making the record of identities of various plant species. The plant parts are dried, pressed and then mounted on this small, thick piece of paper. After this the sheet is labeled at the bottom right corner indicating the name and origin point of the respective mounted species. The collection of these labeled and preserved specimens of dried plants is known as the herbarium or the herbarium can be referred to as the store house of the dried and pressed specimens which are dead and carefully preserved on the sheet of paper called the herbarium sheet. The collection of plants in this manner is of utmost importance to the taxonomic researchers. They help the research in defining the family of any plant.
The standard size of a herbarium sheet is 41cm x 29cm or 11.5 inch x 16.5 inch.

Hence, the correct answer is option (A).

Note: The flora of the world is documented in the herbaria delivering a fixed record of botanical diversity constantly. This record is very important because the constant destruction of habitat and rapid climatic changes are continuously evolving species at a very fast pace. Therefore it is very necessary to keep the records.