My friend always (a) / likes to travel (b) / by the air (c) / since he is a very busy man (d) / no error (e)
the should be removed.
no article is to be placed in between - by post, by air, by sea, by land, by car, by chance, by cheque.
A compromise has been reached (a) / between the centre (b) / and states on the (c) / formula for administrative control over (d) / taxpayers under the GST (e)
article the should be placed before states.
When two different nouns are connected by "and", and article is placed before the first subject, then another article should be placed before the second subject too.
what nice mother (a) / she is, (b) / because she takes care of (c) / every small need of her children (d) / no error (e)
article "a" should be placed before nice mother
Price William (a) / is a heir (b) / to the throne of (c) / the Great Britain (d) / no error (e)
"a" should be replaced with "an"
Wisdom of Vikramaditya (a) / solved many riddles (b) / that people brought to him (c) / for solution (d) / no error (e)
usually before any abstract noun, we never use an article.
however, if that abstract noun refers to individual quality, then "the" article should be placed before the abstract noun.
Indian companies mostly (a) / excel at providing (b) / services to the foreign clients (c) / rather than creating their own IT products (d) / no error (e)
foreign clients are not any particular. hence the should be removed
Rahul's habit of (a) / delaying his work (b) / put his colleagues (c) / into a lot of troubles (d) / no error (e)
The Chinese is a very difficult (a) / language to understand for those (b) / who have never been (c) / to China (d) / no error (e)
articles should not be used before languages.
We should drink (a) / several glasses of the water (b) / daily if we (c) / want to remain healthy (d) / no error (e)
the should be replaced
On my request (a) / Jeetu introduced me (b) / to his friend (c) / who is a singer and scientist (d) / no error (e)