Replace "Mr. Gupta with his wife" by "Mr. Gupta and his wife" . Hence, option (A) is the correct answer.

No error

use plural form ‘pairs’ instead of singular form ‘pair’. Hence, option (C) is the correct answer.

Solution: 2 No sooner … than, hardly/scarcely…when. Example- Hardly had I arrived home when my phone rang. Use ‘when’ instead of ‘then’.

subject ‘demand’ is singular – use singular verb ‘is’ instead of ‘are’. Hence, option (C) is the correct answer.

No error.

Replace ‘master’ with ‘master’s’ .( to do a master’s degree ) Hence, option (B) is the correct answer.

when two nouns “possess” the same entity, only the second takes an apostrophe ( ’ ): Use Rajesh instead of Rajesh’s. Hence, option (B) is the correct answer.

Sentence is based on the structure –If not……then
Part (A) should be 'If not too long then'. Hence option A is correct.

Unless means if this condition is not met (Unless you work hard , you won’t pass. ), Do not use negative word in the clause starting with conjunction unless. The correct usage should be unless you obey in part (A). Hence, option (A) is the correct answer.