1) When a material noun denotes a mass of matter, it is not used in plural form.
The house is built on bricks and stones. (incorrect)
The house is built of brick and stone. (correct).
2) Some nouns have the same form for the plural as well as the singular. Some of them are listed in the examples.
Examples: Sheep, species, deer, aircraft offspring, yoke ,spacecraft, salmon etc.
3) Some nouns are apparently plural in form but singular in use.
Examples : news, economics, physics, mumps, ethics etc.
4) The following nouns are always used in plural : cattle, police, people, vermin, poultry etc.
5) When a plural noun denotes a specific amount, length, weight , quantity etc. considered as a whole , the verb must be in singular form.
Ten thousand rupees is a large amount.
Six kilometers is not a long distance for a runner like you.