Salt is the plural of salt because you wouldn't say salts and if you wanted to say salt as in just one grain say "a grain of salt."
If you specifically need to indicate a large amount, you can add "a lot of" before salt, or you can say cans/jars/shakers/bottles/pinches of salt. Salt is referred to as a noncount noun though, and it doesn't have a plural form in itself.
To complicate the matter, the term "smelling salts" exists, but that's a different kind of mineral, not NaCl.
Bridges is the plural form of bridge.
"Beliefs" does not have a plural form, as it is already plural. Beliefs is the plural form of belief.
There is no plural form for the word, countries. This word itself is a plural.
The plural of "she" is "they", so the plural of "she had" is "they had".
There is no plural form of pupae. Pupae is the plural form of pupa.
Salt is considered a mass noun, which means it is generally used in the singular form. However, it can also be used in the plural form when referring to different types or varieties of salt.
There is no plural form. Do and Do not are verbs
The plural form of him, her, or it is them. (objective pronouns)
Bridges is the plural form of bridge.
The plural form of "is" is "are."
The plural form of "I" is "we."
The plural form of "was" is "were."
"Groceries" is the plural form of "grocery."
"Beliefs" does not have a plural form, as it is already plural. Beliefs is the plural form of belief.
The plural form of mouth is mouths. The plural form of month is months. The Mounth is a range of hills in Scotland and does not have a plural form.
The plural form of the demonstrative pronoun 'that' is those.
The plural form is metres.