1. I applied a kiwi pack on my face.
2. I applied a pack on my face to protect my face.
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Are both sentences correct? Do we have to add 'a' or remove 'a'?
Sentence 1 is fine.
In sentence 2, if you remove "on my face" it'll be fine, too. The repetition is not needed.
=)
Both sentences are grammatically correct; however, they convey slightly different meanings.
1. "I applied a kiwi pack on my face." - This sentence implies that you used a specific pack made of kiwi on your face. The word "a" indicates that it is one pack among potentially many others.
2. "I applied a pack on my face to protect my face." - This sentence indicates that you used any kind of pack for the purpose of protecting your face. The word "a" in this context refers to a general pack, without specifying its contents.
So, to answer your second question, both sentences are correct as they are. The addition or removal of "a" depends on what you are trying to express.