She has spent most of her life helping the poors [Wrong]

GRAMMAR INCORRECT TO CORRECT
Incorrect: She has spent most of her life helping the poors.
Correct: She has spent most of her life helping the poor.

Grammar: Instead of saying 'poor people' we often say 'the poor', using the adjective as a noun. Adjectives used as nouns (and -ed forms used as nouns) do not take a plural ending: 'He is collecting money for the blind.' 'The injured have been taken to hospital.' 

The curtains' colour had faded in the sun. [Wrong]

GRAMMAR INCORRECT TO CORRECT
Incorrect: The curtains' colour had faded in the sun.
Correct: The colour of the curtains had faded in the sun.

We do not normally add - 's/-s' to an inanimate noun [curtains']. Instead, we use an of-phrase 'the end of the road', 'the outskirts of the town', 'the back of the door'.

Note however that time expressions usually take -'s/-s': six weeks' work, a month's salary in advance.

Nouns: Common English Grammatical Errors

Incorrect English: Is Ram still in the hospital?

Correct English: Is Ram still in hospital?

Incorrect English: We visit Ram in hospital.

Correct English: We visit Ram in the hospital.

Some nouns such as school, hospital, prison can refer to a particular place or a type of place. When they refer to a type of place, they are considered to be uncountable and do not need a determiner.

But when they refer to a particular place, they are countable and need a determiner if in the singular form.

In the first example mentioned above, the noun hospital is denoting a type of place; whereas in the second example, the noun hospital is denoting a particular place.

Some of these nouns are university, college, class, church, home, bed, hospital, jail, prison, sea, work.

Note: However, in American English, such type of nouns referring to a type of place use ‘the’ as a determiner.

E.g. Is Ram still in the hospital?