Police would be a concrete noun. You can see police, you can (though I wouldn't recommend it) touch police, you can also hear police. If you are able to use your senses to identify the noun, then it is concrete.
The noun 'police' is a common, abstract, aggregate noun, a word for the group of different people with different roles that make up a law enforcement group. An aggregate noun has no plural form.
Yes, the noun astonishment is an abstract noun, a word for an emotional reaction.
Is undergone an abstract noun
Concrete noun
The abstract noun is criticism.
The noun 'hopefulness' is an abstract noun, a word for an emotion.
The abstract noun is obligation.
Friendship has not abstract noun because It is a abstract noun
Abstract noun of hopeless
The abstract noun form is tourism.
The abstract noun for the adjective quick is quickness.