4. When the pronoun ‘one’ is used, it should be maintained throughout the whole sentence.
One must help his siblings. (Incorrect)
One must help one’s siblings. (Correct)
5. For living people ‘whose’ is generally used and for things that are non-living ‘which’ is used.
Which phone is kept on charging? (Incorrect)
Whose phone is kept on charging? (Correct)
6. ‘Fewer’ is used for denoting number while ‘Less’ is used for denoting quantity.
No less than thirty dogs were. (Incorrect)
No fewer than thirty dogs were. (Correct)