The plural of "classification" is "classifications."
Yes. The word "classification" is singular.
The plural of laboratory is spelled laboratories.
It is commonly accepted in English to use the word 'tsunamis' as the plural because it has been incorporated into the English language. Even though it originated in Japan, it has been adopted in various other languages. Language purists will argue that there is no plural because there is not a Japanese plural for the word, but it is no longer strictly a Japanese word.
The word necessary is an adjective and so doesn't have a plural noun. The noun form is necessity and the plural is necessities.
rainfalls
Yes. The word "classification" is singular.
The word "specie" means coined (precious metal) money. The word "species" (singular or plural) is a scientific classification (taxon) of living organisms.
the classification of a mushroom is a fungus or in the plural sense fungi
The word crises is a plural word; it is the plural form of the word crisis.
There is no plural word for if.
The plural form for the demonstrative pronoun this is these.
A non-plural word, a word (noun or pronoun) that is not plural is singular, a word for just one.
The plural word of delay is delays.
the plural word is comedones
No it's a singular word. A plural word would be "have".
Leukocytes is the plural of leukocyte
The plural noun is raisins.